When producer Robert Evans was trying to coax Roman Polanski to direct Chinatown (1974), he found Polanski thoroughly absorbed with this film, to the extent that he had bought a 50% share in it. Evans eventually lured Polanski by saying that whatever "What" made in its opening week, he would pay him as his salary for directing "Chinatown". Polanski readily agreed to this, expecting "What" to do well as he considered it the best thing he had done up to that point. Unluckily for Polanski, "What" only grossed $64 on its first week.
The character of Nancy was inspired by the Playboy Magazine serial comic "Little Annie Fanny."
On her nude scenes, Sydne Rome said, "At first I really didn't want to take my clothes off, and Polanski, after sending everyone away, yelled at me, 'Are you a Mormon? What's the matter with you? What's with you, huh? Are you a Mormon!!!?' Then again, I think he finally chose me because of this modesty of mine that was shining through. I really felt I was dying! He was even very angry because I didn't want to do Playboy. Go figure. I was twenty-two years old, feeling the influence of my family and coming from puritanical America, I thought if my father saw it he would die of it!"
In 2017 Renate Langer accused Roman Polanski of raping her in 1972, when she was 15, just before and during the filming of this movie. Langer said she met Polanski when she worked for a modeling agency, and he was interested in casting her in a movie. When she visited him in the Swiss village Gstaad, she said he had sex with her in his home, despite her protests. About a month later, Langer told the Times, he called to apologize and offered her a small role in Che? (1972) (where she has a nude scene). While on set of 'What?', Langer said Polanski raped her a second time, despite her efforts to defend herself with a bottle of wine and a bottle of perfume.
#6 on the list "15 Garbage Movies With A Ton Of Skin" published by website TheClever.