Ross Hunter wrote that after he made this film, no theatre managers wanted to book it. Popular movie themes at the time were war films, westerns, or spectacles. Hunter was told by the big movie chains that sophisticated comedies like "Pillow Talk" went out with William Powell. They also believed Doris Day and Rock Hudson were things of the past and had been overtaken by newer stars. Hunter persuaded Sol Schwartz, who owned the Palace Theatre in New York, to book the film for a two-week run, and it was a smash hit. The public had been starved for romantic comedy, and theatre owners who had previously turned down Ross Hunter now had to deal with him on HIS terms.
The first scene that was shot was the one towards the end of the movie in which Rock Hudson drags Doris Day out of bed and carries her through the streets of New York to his apartment. After many takes, Hudson's arms were hurting, so they created a sort of sling which held Day in a crate-like device and hooked over Hudson's shoulders to evenly distribute her weight.
At the diner, after Jonathan (Tony Randall) slaps Jan (Doris Day), a truck driver (John Indrisano) punches him in the jaw. In an interview, Randall said that he and Indrisano practised the punch many times and Indrisano assured him that he would not be hit. During the take, Indrisano misjudged and Randall was actually struck and knocked unconscious.
Michael Gordon had hoped to make a sequel to this movie in 1980. It was to be set 20 years after the events of 'Pillow Talk' and involve Brad and Jan having their first daughter, played by Kristy McNichol with Gregory Harrison as her boyfriend, and getting a divorce, which would allow Jonathan to have another chance of wooing Jan. Jan schemes to get Brad back, while he does some scamming of his own. Doris Day and Rock Hudson were both interested in returning for the sequel, but it unfortunately never materialized, with Day's retirement from acting being one of the reasons why.
Spanish TV screened "Pillow Talk" on 20th July 1969 while everybody was waiting for the Apollo landing on the Moon. Suddenly, the film stopped and Spanish people could see the landing live. The film was not reshown on TV until 1999, when Spanish viewers could, at last, see the ending!
Despite being contractually bound by Universal to do the film, Rock Hudson consistently declined it, fearing it was too dirty and would harm his masculine image. Doris Day finally talked him into starring in it, and subsequently it became one of his biggest hits.
The trivia item below may give away important plot points.
The original ending involved Jan, after using the trick switch to lock the door to Brad's apartment, simply saying, "All apartments look alike in the dark", before the movie abruptly ended. This open ending was changed to the one used in the final film, which shows that Brad and Jan got married and are now expecting a baby together.