Trivia

According to the 1974 biography "Barbra Streisand: The First Decade", this was originally envisioned as a three-hour "road show" extravaganza, and included many sequences of Daisy's other lives (photos of which were printed in some pre-release promotions), but director Vincente Minnelli and the studio felt it would be too long, especially since musicals had already begun to fail at the box office. In addition to all but the briefest of Jack Nicholson's scenes being cut, a musical number sung by him and Streisand, "Who Is There Among Us Who Knows?," was also cut, as well as "Wait Till We're Sixty-Five," a duet between Larry Blyden and Barbra Streisand. Producer Howard W. Koch conducted a search for the deleted footage in 1994, particularly Nicholson's song, which he wanted to showcase during the AFI tribute to the actor. Nothing turned up at Paramount. Koch asked Streisand and Minnelli's widow if they had remnants of the cut footage, but neither did. Koch determined that if the film still exists, it's probably in a mislabelled canister.

Paramount offered Yves Montand $200,000 for the role of Dr. Marc Chabot. Uneasy about playing another French lover role, Montand made a counteroffer of $400,000, "just to see what they say". To his surprise, Paramount accepted.

The original Broadway production of "On A Clear Day You Can See Forever" opened at the Mark Hellinger Theater on October 17, 1965, ran for two hundred eighty performances and received Tony Award nominations for Best Score, Best Actor (John Cullum) and Best Actress (Barbara Harris).

Richard Harris was briefly considered to play Marc Chabot.

According to Marc Elliot's "Nicholson: A Biography", Jack Nicholson only accepted the role because of the money and his desire to act in something more mainstream than the films he was doing (at the time, Easy Rider (1969) was in the editing process). The role he plays, Tad, does not appear in the original play. Studio head Robert Evans had insisted upon adding a counter-culture character to the film version, and his only choice for the role was Nicholson. The actor accepted the role but didn't enjoy the experience.