The stage version of "Plaza Suite" by Neil Simon originally had four acts instead of three. The act that was cut was entitled "Visitor from Toledo", and was intended to open the play. Simon once described the act to the Newark Evening News as being "...about a man who came to New York from out of town and lost his luggage. He got there in the middle of a transit strike. It was snowing. So after he had checked into the Plaza [Hotel] he had this monologue. We put Plaza Suite into rehearsal, and after about the fifth day [director] Mike Nichols said, 'We just have too much show here. If we include that monologue, the curtain will be coming down at midnight.'" Simon later re-worked and expanded that story into the film The Out of Towners (1970).
This film's screenwriter and source playwright Neil Simon once said of this movie: "I didn't like the cast. I didn't like the picture. I would only have used Walter in the last sequence and probably Lee Grant. I think Walter Matthau was wrong to play all three parts. That's a trick Peter Sellers can do. I have to accept some of the blame for the film. I kept all the action in one room. It was rather confining. We could have gone into other suites. I didn't think it out, but I learned from that."
Maureen Stapleton is the only original Broadway cast member in the film. On Broadway, she played all three lead females roles of Karen, Muriel and Norma.
Jesse Kiplinger was based on Neil's brother, Danny Simon. Danny tried to romance an ex-girlfriend, but she just wanted to hear about celebrities he knew.
Maureen Stapleton recreated ONE of her three roles from the stage version. Like the male roles, Neil Simon wrote all three female roles to be played by one actress. George C. Scott and Maureen Stapleton originate all of the roles in the play; Walter Matthau took over for Scott in all three roles - Stapleton kept her role from the first act; the other two roles went to Lee Grant and Barbara Harris.