Submitted by Taiga

Stanley’s (Marlon Brando) cruelty towards his wife’s sister Blanche (Vivien Leigh), culminating in a rape, drives Blanche to a nervous breakdown. Stella (Kim Hunter) and Stanley have Blanche commited to a mental institution. Stella takes her newborn son and leaves Stanley.
(In the eponymous Tennessee Williams play upon which the film is based, Stella stays with Stanley in the end.)