In the sequence where they have to say magic words to summon the invisible swordsman, one of Steve Martin's magic words is "Hfuhruhurr," his character's name in The Man with Two Brains.
Randy Newman, who wrote some of the the songs for this movie, was the voice of the singing bush. This was lifted directly from the Holy Bible's book of Deuteronomy. Moses' (the Amigos') vision to guide the oppressed Egyptians (Santa Pocans) into freedom.
Originally the movie was supposed to star Steve Martin, Dan Aykroyd and John Belushi. Martin mentioned it in a Playboy interview published January 1980, referring to the movie as 'The Three Caballeros'.
The injury that Steve Martin's character gets from the first gunshot wound is in his left arm, in the same spot he kept getting shot in his earlier film, Dead Men Don't Wear Plaid.
Carl La Fong (actor/stunts) is the name used to great comic effect when W.C. Fields is questioned about that character's whereabouts in It's a Gift: Insurance Salesman: Do you know a man by the name of LaFong? Carl LaFong? Capital L, small a, Capital F, small o, small n, small g. LaFong. Carl LaFong. Harold: No, I don't know Carl LaFong - capital L, small a, capital F, small o, small n, small g. And if I did know Carl LaFong, I wouldn't admit it!
In his memoir, Life Itself, film critic Roger Ebert recounted appearing as a guest on The Tonight Show Starring Johnny Carson alongside Chevy Chase who was promoting the film. During the interview, Ebert was asked what his least favorite film of the holiday season was, he replied ¡Three Amigos!. Chase said "looking forward to your next picture" but later confided with Ebert backstage that he didn't "think it's so hot, either."
"Nederlander" is Dutch for 'Dutchman (from the Netherlands)'. Interestingly, the film's assistant production coordinator Sharon Nederlander bears the same name.
At one point, El Guapo harasses Jefe about the meaning of the word "plethora", in relation to how many piñatas he had. In reality, "plethora" is a commonly misused word, meaning "too much" of something rather than simply a lot of something. So instead of telling El Guapo that he had enough piñatas, Jefe actually told him that he had too many piñatas.
According to Mexican-American film historian David Maciel (El bandolero, el pocho y la raza, 1998) the film was considered demeaning by Mexican film authorities so that its release was never authorized.
John Landis said in an Empire magazine piece on the film that it was taken out of his hands in post by the studio and heavily edited. It had its first scene cut for instance.
The trivia items below may give away important plot points.
The basic story and quite a few scenes borrow heavily from Akira Kurosawa's "Seven Samurai". (Seven Samurai): Village terrorized by bandits; A few villagers goes into town to find help; They have very little to offer; No help from towns people; They find "warriors"; They prepare defenses (among them water filled trenches); Large climactic battle; The leader is the last of the bandits to die; Three prepare to leave the village; One looks back at the girl he fell in love with (though Three amigos has a slightly happier version of what happens then).