Which 1975 film won Best Picture and starred Jack Nicholson as a patient in a mental institution?

The 1975 Best Picture winner starring Jack Nicholson as a patient in a mental institution is One Flew Over the Cuckoo's Nest.

Nicholson plays Randle McMurphy, a rebellious prisoner who pretends to be mentally ill to avoid hard labor and is sent to a psychiatric hospital. There, he clashes with Nurse Ratched, played by Louise Fletcher, whose rigid control over the ward becomes the film's central conflict. Miloš Forman directed the film from Ken Kesey's 1962 novel.

The production was filmed largely at the Oregon State Hospital, an actual psychiatric institution in Salem. The setting helped give the film its realistic atmosphere, and several performers observed hospital routines while preparing for their roles. The cast also included Brad Dourif, Danny DeVito, Christopher Lloyd, and Will Sampson.

The film won all five major Academy Awards: Best Picture, Best Director, Best Actor, Best Actress, and Best Adapted Screenplay. It was only the second film to achieve that sweep at the time. Its title comes from a counting rhyme recited by Chief Bromden, one of the hospital's patients.