Sidney Lumet had the actors all stay in the same room for hours on end and do their lines over and over without taping them. This was to give them a real taste of what it would be like to be cooped up in a room with the same people.

Lee J. Cobb's character insults Juror #12 by calling him "The Boy in the Gray Flannel Suit." One year before the release of 12 Angry Men Cobb starred in The Man in the Gray Flannel Suit, which also featured Joseph Sweeney (Juror #9).

Jack Lemmon appears in Mister Roberts with Henry Fonda, in which he takes over Fonda's position of Cargo Officer when Fonda is transferred off the USS Reluctant. In the 1997 remake 12 Angry Men, Lemmon plays the same juror that Fonda played in the original 12 Angry Men.

Reginald Rose's TV play script was left virtually intact in its move to feature film.

Henry Fonda disliked watching himself on film, so he did not watch the whole film in the projection room. But before he walked out he said quietly to director Sidney Lumet, "Sidney, it's magnificent."

Henry Fonda immediately complained to Sidney Lumet about the cheap backdrops outside the jury room windows when he walked on set. "They look like shit. Hitch had great backdrops, you could walk right in them," said Fonda, referring to the previous film he made with Alfred Hitchcock, The Wrong Man. Lumet assured him that the director of photography Boris Kaufman had a plan to make them work.

Henry Fonda was asked by United Artists to make this film, so he did it as both actor and producer. He was, however, very frustrated at being producer and decided never to do so again.

Henry Fonda, who symbolically wears white throughout the film, personally asked Sidney Lumet to direct the movie adaptation, having been impressed with his work on the TV version, Twelve Angry Men.

After a short but rigorous rehearsal schedule, the film was shot in less than three weeks for a budget of just $350,000.

After Juror #10's prejudicial rant about the poor and everybody turns their backs on him, Juror #4 tells him to "sit down and don't open his mouth again." Juror #10 thus doesn't say anything for the rest of the film (when prompted for his final vote he shakes his head "not guilty," and doesn't verbalize anything).

All but three minutes of the film was shot inside the bare and confining, sixteen by twenty-four foot "jury room".

As shooting of the film went on, director Sidney Lumet gradually changed to lenses of longer focal lengths, so that the backgrounds seemed to close in on the characters, creating a greater feeling of claustrophobia.

As the film failed to make a profit, Henry Fonda never received his deferred salary. Despite this setback, Fonda always regarded 12 Angry Men as one of the three best films he ever made, the other two being The Grapes of Wrath and The Ox-Bow Incident.

At the beginning of the film, the cameras are all positioned above eye level and mounted with wide-angle lenses to give the appearance of greater distance between the subjects. As the film progresses the cameras slip down to eye level. By the end of the film, nearly all of it is shot below eye level, in close-up and with telephoto lenses to increase the encroaching sense of claustrophobia.

Because of the demands of the film's low budget, if the lighting was set up for a shot that took place from one particular angle, all the shots from that same angle had to be filmed then and there. This meant that different sides of the same conversation were sometimes shot several weeks apart.

Because the painstaking rehearsals for the film lasted an exhausting two weeks, filming had to be completed in an unprecedented 21 days.

Debut of John Fiedler.

Despite numerous critical accolades, the film was not a box office success on first release.

For many years, only the first half of the kinescope of the TV version of "Twelve Angry Men" broadcast live on Sept. 20, 1954 (Twelve Angry Men) was thought to survive, and had been in the possession of the Museum of Television and Radio since 1976. In 2003 a complete 16mm kinescope was discovered in the collection of Samuel Leibowitz (former defense attorney and judge) and was also acquired by the museum.

In 12 Angry Men Lee J. Cobb's character was played by George C. Scott. Making it the second time Scott followed Cobb in portraying the same character. He did it previously, playing the character of "Lt. Kinderman" in The Exorcist III, the same character Cobb played in the original film The Exorcist.