At one point during rehearsals, director Sidney Lumet felt that Sir Ralph Richardson wasn't really getting the proper measure of his character, James Tyrone. Lumet took Richardson aside and launched into a forty-five minute lecture about his character's motivations. Richardson finally stopped him by saying "I see what you mean, dear boy, a little more cello, a little less flute". Lumet confessed to being enormously impressed with this way of expressing it.

Filmed entirely in sequence after three weeks of rehearsal.

According to Katharine Hepburn biographer Charles Higham, she became so upset with Dean Stockwell when he showed up on the first day of shooting with a bottle of vodka, she almost struck him. When she discovered he found the set very cold, she bought him a coat, which he later found in his dressing room.

Marlon Brando was offered the role of Jamie Tyrone.

At two hours and fifty-four minutes, this is Sidney Lumet's longest movie.

Jason Robards, Jr. reprised his Broadway role as James Tyrone, Jr., for which he was nominated for the 1957 Tony Award for Best Featured Actor in a Play. He also played James Tyrone, Jr. on Broadway and on television, in A Moon for the Misbegotten (1975). In his later career, Robards played James Tyrone, Sr. in several productions of "Long Day's Journey Into Night," including a 1988 Broadway revival at the Neil Simon Theater.

This movie takes place in August 1912.

The cast includes two Oscar winners: Katharine Hepburn and Jason Robards, Jr.; and two Oscar nominees: Sir Ralph Richardson and Dean Stockwell.

The Broadway play by Eugene O'Neill opened at the Helen Hayes Theater in New York City on November 7, 1956 and ran for three hundred ninety performances. The stage production included Florence Eldridge, Fredric March, and Katharine Ross and won the 1957 Tony Award for the Best Play and the Pulitzer Prize in Drama in 1957.

Sir Ralph Richardson and Jason Robards, Jr. played the same role in "A Doll's House", Dr. Rank.

Christine Lahti named this movie and The Apprenticeship of Duddy Kravitz (1974) as her favorite movies in an American Film Institute poll.