A number of people have been identified as (or implied to be) lesbian, gay, bisexual, and/or transgender (commonly abbreviated LGBT).
Lesbians are homosexual women. Gays are homosexuals in general (in this context, homosexual men). Bisexuals are attracted to both genders, sometimes known as bi. Transgender people are people who don’t believe they fit the sex assigned at birth.
So far, no characters have been described as asexual, demisexual, intersex, genderqueer, genderfluid, or other.
Kang and Kodos are both gender ambiguous. While Kang is usually shown as male (although he may be intersex), Kodos’ gender is uncertain: Kodos has a male voice and is called male in “E.T. Go Home”, yet is also called “sister” and wears female clothing in Tapped Out. However, Kamala is explicitly shown as female. It could also be possible that Kodos was referred to as "sister" for comic purposes.
- Patty Bouvier - Almost married Veronica. However, Veronica was actually a man named Leslie, so the wedding was called off. However, Patty has been shown with men, i.e. Principal Skinner, although this was before she was established as homosexual. In Treehouse of Horror III, she says, “there goes the last lingering thread of my heterosexuality” after seeing Homer naked, but this is a non-canon episode and could simply be given the line for comic effect. She has been noted to be attracted to Edna Krabappel, as she imagines her when she has to kiss Homer to break up Selma and Abe. She also dated a girl named Evelyn in "Livin La Pura Vida".
- Evelyn - She dated Patty in "Livin La Pura Vida". She ended up breaking up with Patty after she became friends with Homer but reunited with her at the end of the episode.
- Paula - Hinted as being attracted to Marge and since most of her room contains stereotypical lesbian things. Towards the ends of the episode reveals she has a wife. ("Marge the Lumberjill")
- Megan Matheson - Reveals having a wife.
Hinted to be lesbian
- Martha - Hinted to be attracted to the assistant librarian.
- Librarian - Hinted to be attracted to Martha. Though it isn’t confirmed.
Openly gay characters
- Comic Book Gay - Comic Book Guy's gay cousin. He likes "certain kinds" of comic books.
- John - A nostalgia store owner who befriends the Simpson family. He is voiced by John Waters who is openly gay in real life.
- Roscoe - Manager of the Ajax Steel Mill. He and his workers are all gay, and at breaks, they turn the mill into a gay nightclub.
- Steel Mill Workers - Gay workers who work for Roscoe. 
- Angelo - A builder who was employed to remodel the Simpsons' kitchen after Homer's failed attempts. When Homer told him to kiss Marge he says that he is gay but the subcontractor does that for him.
- Grady and Julio - A gay couple that Homer roomed with; they later broke up. Grady is voiced by comedian and actor Scott Thompson who is openly gay in real life. Hank Azaria (voice of Julio) previously used the same voice for another gay character named Agador Spartacus in the 1996 comedy film titled The Birdcage. This reference is further grounded in the episode's aptly parodied title, The Burns Cage.
- Thad - Marries Julio (with Homer as the officiant) subsequent to Julio's and Grady's breakup.
- Grizzly Shawn - Becomes interested in Moe. He later married Barry.
- Barry - A husband of Grizzly Shawn.
- Dewey Largo - It was first assumed in "See Homer Run" when he claimed that he and Waylon Smithers were carpooling. In "Flaming Moe", he announces to his music class that he is running away with the love of his life, who is a man. He also has an exaggerated lisp.
- Waylon Smithers - There are numerous references to Smithers' orientation (or at least his fixation on Mr. Burns) and his efforts to keep it a secret. However, a blatant example occurs when Smithers boots up his home computer and animation of Mr. Burns appears, saying (in obviously cobbled-together sound clips), "Hello, Smithers. You're quite good at turning me on." Smithers then says to Lisa (who was standing behind him), "Um, you should probably just ignore that." Smithers was first shown to be openly gay in Flaming Moe when he helps reopen Moe's tavern as a gay bar. Smithers comes out in The Burns Cage. He has been considered as gay rather than ‘Burns-sexual’, notably when 2 strippers came up to him and he started cowering in fear.
- Dewey - An ex-boyfriend of Dewey Largo.
- Elton John - He is openly gay in real life and has been married to Canadian filmmaker David Furnish since 2005.
- Philip Hefflin - A photographer who was interested in Abraham Simpson and claims that women disgust him.
- Svenjamin "Sven" Golly - Upon meeting Marge, he says, "Ugh, where were you when I was straight?".
- Just Stamp the Ticket Man - In "The Fat Blue Line", it's revealed that he is gay for Homer Simpson.
- Gay Colonel - Colonel who dates with Hans Moleman.
- Unnamed smoking man - Moe tried to steal his watches, but when the man noticed him, Moe said that he had been just coming on to him. The man took Moe's hand and said that they could go back to his place.
- Stuart - A close friend to Waylon Smithers.
- Llewellyn Sinclair - Is seen in the crowd of gay men.
In the closet
- Unnamed Latino Man - When he saw Homer's graffiti tag of "El Homo", he said, "If only I had your courage, señor."
- Raoul - Women disgust him and he becomes interested in Abraham Simpson.
Hinted to be gay
- Rod and Todd Flanders - Ned Flanders gave Bart Simpson money for not outing them in "Bart to the Future"; they had mustaches and were seen refurbishing furniture in denim shorts and white sleeveless shirts. Also, both brothers have been shown to exhibit stereotypically gay behavior, such as holding hands while skipping. Also, Rod shouted to Ned that Marge “made me gay”, which resulted in Marge covering for him, due to Ned’s anti-gay viewpoints. But this was just Bart making Rod say this, as he told him it means that you used to be afraid, but now you're not. Additionally, Jenda Simpson, a character seen in other future-centered episodes, once dated Todd.
- Karl - Kissed Homer on the lips after stating that his mom taught him to never kiss a fool and he was voiced by Harvey Fierstein, one of the first openly gay celebrities. However, it should be noted that Karl is implied to be of German origin, and men kissing men doesn't necessarily equate to homosexuality as much as just respect in some European countries, but generally not on the lips, rather on the cheek. Karl also patted Homer on the behind after giving him a pep talk, but in the context of the situation, it could easily be considered a comradely gesture rather than an affectionate one. He was also seen in the background in the episode Flaming Moe, and dancing with Jacques in the “Do the Bartman” music video.
- Cecil Terwilliger - In the quest "Say 'Cheers'" Cecil is shown to be attracted to Moe Szyslak calling him beautiful, and making several other homosexual statements.
- Lady Gaga - She is openly bisexual in real life (which is hinted in the hit single "Poker Face") and even kisses Marge Simpson in "Lisa Goes Gaga", much to Marge's surprise. However, Marge is straight as far as we know.
- Verity Heathbar - Leaves her husband Charles for Patty, who says that they were brought together by their hatred of Homer. Patty has never had a confirmed marriage yet, however.
- The dwarfs in Lisa's Snow White story - Sing that they're bi at the end of the story.
Hinted to be bisexual
- Rainier Wolfcastle - Possibly bisexual since he has his early gay porn films located within his bedroom in "The Strong Arms of the Ma", although these may have been made for money (i.e. gay for pay) and not as a reflection of his real sexuality.
- Leprechauns - two of them seen holding hands at a St. Patrick’s Day festival. However, one of them married a gypsy woman in “Hex and the City”.
- Duffman - Slept with Titania, who was competing in a bartending contest that he was judging. However, Bart mentions that Duffman is supposedly in a long-term gay relationship after seeing him dining with Booberella. He is later in a relationship with Grady. It should be noted, however, that there are several different actors portraying Duffman, and not all of them necessarily have the same sexual orientation. Also, some of the actors are now dead.
- The Sea Captain - Apu delivers pornographic magazines to keep the Sea Captain's crew from resorting to situational homosexuality for about ten minutes, at least. However, the Captain is also seen taking pictures of Selma and Patty in the nude to cope with being out at sea.
- Santa's Little Helper - Intrigued by male dogs at the Springfield Gay Pride Parade. However, he mated with both She's the Fastest and Rosa Barks, both of whom were definitely female as both unions produced puppies.
- Ralph Wiggum - In The Simpsons Movie, he declares, "I like men now!" after seeing Bart naked on a skateboard. However, Lisa Simpson was his first crush. It should be noted, though, that nothing Ralph says about himself is reliable since his understanding of everything is questionable.
- Martin Prince - Generally effeminate. He is accused of being gay by Nelson and protests, "I'm not anything yet!"; but has a robot boyfriend in the future. On the other hand, he did have an attraction to Princess Kashmir on seeing Bart's photo of her dancing with Homer, even referring to it as being "quite exciting" and calling her a "sexy lady" when he asked Bart who she was. When he imagines himself as a basketball player in "Replaceable You" he is holding hands with both a male and female cheerleader.
- Lisa Simpson - (Note: all examples here at from episodes and scenes showing the future, and thus are not considered canon.) In the episode "Holidays of Future Passed", a montage of photos were featured to show a glimpse of what’s to come for the Simpsons family. Lisa is shown intimately holding hands with two women in one photo, then with a different woman in another photo. She is later shown married to Milhouse Van Houten and having a child with him, and possibly marrying Ralph Wiggum. She has also dated several other boys. In the episode Gorgeous Grampa, Homer is flipping through the reality shows, to Lisa's disgust. However, when Homer and Lisa keep flipping through channels and see a reality show on gay marriage she says 'Well' and thinks about it. Al Jean also teased that a future-set episode in Season 29 would feature Lisa ending up with a woman. However, Mr. Lisa's Opus is ambiguous about it. The episode "Bart to the Future" contradicts this when a then 38-year-old Lisa campaigns and wins to become "the first straight female President" of the United States.
- Milhouse Van Houten - While Dr J. Loren Pryor discusses problems with Bart in kindergarten, he mentions about Bart's “flamboyantly homosexual tendencies” but then realized that it was Milhouse's file instead of Bart. However, Milhouse has a crush on Lisa and has dated other girls such as Samantha and Greta.
- Gil Gunderson - Although once married to Shirley Gunderson, he is shown in Tapped Out wearing a Pride outfit.
- The first, the second and the third of The Cool Moms - They all are married and have sons, but when Marge abandons the club, they start kissing and hugging each other.
- Shauna Chalmers - She is implied to be bisexual as Dolph said that she invited 200 guys and 7 girls to make out with her via a SpringFace message.
- Lenny Leonard - Despite having a girlfriend, he is hinted to be attracted to Carl.
- Carl Carlson - Despite having a wife, he is hinted to be attracted to Lenny.
- Barney Gumble - In the bomb shelter he complains about being touched but he was fine with it when he finds out it was Principal Skinner. He dated Daria before, however, it could be his drunkenness that causes this.
- Hans Moleman - He sadly states that “nobody’s gay for Moleman”. However, he once dated Selma, so whether or not he is secretly gay or bisexual is up for debate.
- Edna Krabappel - while she has dated many men and was married to Ned Flanders, in "The Ned-liest Catch", it is revealed she dated Patty Bouvier once. When Ned is about to kiss Edna in an episode, he envisions all the other people she has kissed. Patty's face comes up and says it was an "experiment".
- Otto Mann - He was almost married to his girlfriend but he is seen together with Julio in the episode Bart the Bad Guy, The Hateful Eight-Year-Olds, and The Dad-Feelings Limited.
- Moe Szyslak - In the episode "Flaming Moe" kisses Smithers, stating: “Not bad, like frisbee golf, I’m glad I tried it once.” Moe has dated women in the past, and has tried to date and marry Marge.
- Helen Lovejoy - In the episode "Sky Police", Helen and Timothy are role-playing when Marge knocks on the door. Helen asks: “Is that a woman’s voice? Send her in.”
- Homer Simpson- In the episode "Three Gays of the Condo", he is kissed by Grady, and later asks himself if it was the best kiss he had that night. He is also married to Marge and has been attracted to several other women.
- Jacques Brunswick who is seen dancing with Karl in the "Do the Bartman" music video.
- Sara Sloane - When the director asks if she is okay with kissing a girl, she agrees without any second thoughts. She is also attracted to Ned Flanders and sleeps with him.
- Rod Flanders - Exhibits stereotypically gay behaviour and in "Bart to the Future", Ned makes a reference to "outing" him. However, in "A Star is Born Again", he gazes at a scantily-clad Sara Sloane and asks Ned where babies come from, possibly expressing a desire to have children with her.
- Todd Flanders - Like his brother, he exhibits stereotypically gay behaviour and Ned makes a reference to him being "outed" in "Bart to the Future". However, in other future-centered episodes, it's implied that Jenda Simpson dated him in the past.
- Judge Constance Harm - Indicates that she was assigned male at birth.
- Brunella Pommelhorst - Principal Skinner said she is taking a leave of absence to return to Springfield Elementary as a male shop teacher, but she returned in later episodes still identifying as female.
- Stanlerina - She is Helen Lovejoy's cousin who was assigned male at birth, but transitioned to female at some point in her life.
- Wallis Wilkes-John.
Hinted to be transgender
- Waylon Smithers - Smithers hinted at possibly being transgender when Marge was selling prescription medication at a garage sale and he bought bottles of estrogen for "a friend...who's trapped in the body of another friend." He also hints at transgender tendencies in "When You Dish Upon a Star" when he asks Kim Basinger where to get red pumps similar to those her character wears in LA Confidential, and also in "Weekend at Burnsie's" where Smithers, while stoned from smoking a joint of marijuana in order to allow Homer to keep his vow of not using marijuana after quitting it, proceeded to dress up as Judy Garland and suggested that Homer dress up as Mickey Rooney before realizing after Homer noted that the latter was of 60 Minutes fame that Mr. Burns had been gone for over an hour, far too long regarding his bath. Although not a true hint, the end credits for "Dial "N" for Nerder" had among the "cast" Smithers dressed up in drag as the "wife" of Mr. Burns. In "Frink Gets Testy", when Jonathan Frink searches for Bart's file, Smithers’ file is seen where it also says soon to be Wanda.
- Dewey Largo - Sought gender reassignment surgery from Dr. Nick, but because Nick had the surgery files mixed up, Largo ended up getting an operation intended for Moe, which made him shorter (Moe was able to stop Nick from performing any kind of surgery on him).
- Francine Simpson - Homer Simpson's history of Francine Simpson implied that Francine is a trans woman (also known as Mother Shabubu) who transitioned in 1976.
- Martin Prince - In Holidays of Future Passed, Adult Lisa gets a Facebook-like friend request from Adult Martin Prince, known as Martia Princess before he turned back into a man named Martin Prince. He has stereotypical feminine behaviour for a man
- Helen Lovejoy - In Wedding for Disaster the Parson of the Church mentioned to Reverend that he remembers when Helen was Harold Schwarzbaum. This could indicate that she was born with a traditionally male name rather than being transgender, as she presumably gave birth to Jessica Lovejoy.
- Lenny Leonard - In The Man Who Came to Be Dinner he is shown dressed as Seven of Nine from Star trek voyager. In Revenge is a Dish Best Served Three Times, Bartman mistakes him for the villain Poison Lenny and he replies with, "I'm not a villain, I'm a transvestite"
- Fat Tony - in "Mr. Spritz Goes to Washington" Tony is seen on a private jet with his goons watching "The Divine Secrets of the Yaya Sisterhood" and sobbing into his hand as he says "why was I born a man"
Hinted to be non-binary or intersex
- Dubya Spuckler - Brandine tells her children in the episode "Hail to the Teeth" that they prefer they/them pronouns (due to the fact that they absorbed a twin in the womb). They could be the first non-binary character on the show.
- Gay Neighborhood, a neighbourhood of LGBT people
- There's Something About Marrying
- Homer Is Where the Art Isn't
- The Color Yellow
- Flaming Moe
- Homer's Phobia
- Sleeping with the Enemy
- Three Gays of the Condo
- Lisa vs. Malibu Stacy
- That '90s Show
- Large Marge
- Catch 'Em if You Can
- Simpson and Delilah
- Homer Simpson, This Is Your Wife
- Homer and Lisa Exchange Cross Words
- Marge and Homer Turn a Couple Play
- I'm with Cupid
- Bart's Inner Child
- Jaws Wired Shut
- Two Dozen and One Greyhounds
- Today, I Am a Clown
- The Simpsons Movie
- I Love Lisa
- Homer's Night Out
- Moms I'd Like to Forget
- Homer the Smithers
- Secrets of a Successful Marriage
- The Parent Rap
- We're on the Road to D'oh-where
- Eeny Teeny Maya, Moe
- Lisa's First Word