'Sandra Dee', Geraldine Chaplin, Yvette Mimieux, Tuesday Weld, Sue Lyon and 'Nancy Sinatra' were all mentioned in the press for the role ultimately played by Jane Fonda.
Mildred Natwick and Herb Edelman also appeared in the Broadway production of "Barefoot in the Park" (1963-67).
Neil Simon based this story on his first marriage.
Robert Redford starred in both the Broadway play and this film version. His leading lady on Broadway was Elizabeth Ashley.
A running gag is the absence of an elevator to get to the newlyweds' 6th-floor apartment; new arrivals are out of breath throughout the film. For its release in France, however, the dubbed dialogue placed the apartment on the 9th floor (equivalent to the 10th floor in the US), since in France, older buildings with six stories and no elevator are not uncommon and audiences wouldn't have understood why climbing the stairs was so arduous.
The fictional address of the apartment is 49 West 10th Street.
The film role of 'Corie Bratter' was originally offered to actress Natalie Wood who had already played opposite Robert Redford in two movies. Wood declined the offer though, because she wanted to take time off.
The original Broadway production on which this film is based opened at the Biltmore Theater on October 23, 1963, ran for 1530 performances and was nominated for the 1964 Tony Award (New York City) for the Best Play.
Mildred Natwick and Herb Edelman recreated their Broadway roles in this movie version.