When actor Robert Redford was offered the lead male role in the film, he was surprised. Redford had played the part on Broadway and did not like the idea of repeating himself. Redford believed that it was standard practice for players in Broadway productions to not be considered for parts they had created on the stage for the Hollywood movie version. However, Redford decided to do the film.
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.
This play "Barefoot in the Park" was based on the first early weeks of Neil Simon's first marriage to Joan Baim. Similarly, Simon's later play "Chapter Two" was based on the early part of Simon's marriage to actress Marsha Mason which was Simon's second marriage.
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.
When Jane Fonda is shown going up the stairs to her apartment, they used the same footage of her for every floor she climbs. As she nears the top of the stairs, every hallway flooring (right beside the spindles), has the exact same damage done to it, and a wrinkle or tear in the hallway carpet runner is in the exact same place on every level.
Robert Redford had effectively given up acting prior to filming this. Disillusioned after the relative failure of "This Property is Condemned" " The Chase" and " Inside Daisy Clover ", he quit Hollywood and spent a year travelling around Spain and Greece. It was only after Paramount threatened to sue him over certain " contractual obligations " that he returned home to star in this.
The New York park that is referred to in the film's title is not Central Park, as many people often think who have not seen the film, as the movie is set in New York, Central Park being the city's most famous park, but actually is New York's Washington Square Park.
Redford, who was already familiar with the script and how the characters should be portrayed, worked well with Fonda. If she needed redirection he would take Saks aside, make the point in private, and then Saks would coach her.
This film was made and released about four years after its source stage play of the same name by Neil Simon was first performed in 1963. The original Broadway production opened at the Biltmore Theater on 23rd October 1963 and ran for 1530 performances until 25th June 1967 which was a month after the film opened in the USA. The play was nominated for four Tony Awards in 1964 including Best Play, Best Actress - Elizabeth Ashley, Best Producer (Dramatic) - Arnold Saint Subber and Best Director (Dramatic) - Mike Nichols, it winning only for the latter category. Robert Redford, Mildred Natwick and Herb Edelman recreated their Broadway roles in this movie version. The play's Broadway run more than doubled the season of Simon's previous play, "Come Blow Your Horn". The play's setting described in the play's intro says: "The Bratter's apartment on East 48th Street, New York City. The present".
The amount of time Fonda and Redford spent in the hotel on their honeymoon without coming out was five days. The hotel record was six days. The record was nine days (this is what the maid says) and they spent six days in the room.