Spike Lee originally wanted Robert De Niro for the role of Sal (Salvatore Fragione). But De Niro turned down the part, saying that it was too similar to many of the parts he had played in the past. In the end the part went to Danny Aiello.
The key scene when Danny Aiello and John Turturro talk alone approximately midway through the film was partly improvised. The scripted scene ended as the character Smiley approached the window. Everything after that until the end of the scene was completely ad-libbed.
Radio Raheem's explanation of the love hate rings he wears is an homage to the speech that The Preacher gives in The Night of the Hunter (1955). Robert Mitchum's preacher has tattoos on his hands that say "Love" and "Hate."
The scene in which Sal and Buggin Out argue about there being no African Americans on the wall of the restaurant--only "American Eye-Talians" --is somewhat ironic, as Giancarlo Esposito is Italian-American.
On both an interview and the audio commentary the Criterion DVD of the film, Spike Lee says that the project was originally at Paramount, but the studio was worried about the climax and wanted it toned down. Lee refused, and in the same weekend Paramount turned the project down, Universal picked it up for distribution.
Ice Cube sampled Pino's "You gold teeth, gold chain wearing, fried chicken and biscuit eating, monkey, ape, baboon, big thigh, fast running, high jumping, spear-chucking, three-hundred-and-sixty-degree basketball dunking, titsun, spade, mulignan. Go the fuck back to Africa. Go the fuck back to Africa. Go the fuck back to Africa..." rant for his 1990 song "Turn Off The Radio."
The entire shoot took place on one commandeered block in Brooklyn. Extra care was taken to ensure the experience was palatable to the residents of that block and the production even hired a couple residents on that block.
The trivia item below may give away important plot points.
In the original scripted ending, Sal and Mookie reconcile. Sal, although upset, tells Mookie that he understands that Mookie had to do the right thing. Spike Lee changed the ending during filming and has never explained why he did.