Fassbinder was born in Bavaria in the small town of Bad Wörishofen, on May 31, 1945, three weeks after the Americans entered the town and the unconditional surrender of Germany. The aftermath of World War II deeply marked his childhood and the life of his family. Fassbinder, in compliance with his mother's wishes, later altered the date of his birthday to 1946 in order to enhance his status as a cinematic prodigy. It was towards his death that his real age was revealed confronting his passport.
Born into a cultured bourgeois family, Fassbinder had an unconventional childhood about which he would later express grievances in interviews. At three months, he was left with a paternal uncle and aunt in the country, since his parents feared he would not survive the winter with them. The child was a year old when he was returned to his parents.
In 1951, after his parents divorced Rainer stayed with his mother, who later under the name of Lilo Pempayt or under her own name played supporting roles in many of his films.