The crash diet that Cregar followed for his roles in "The Lodger" and "Hangover Square" (which included prescribed amphetamines) placed a strain on his system, resulting in severe abdominal problems. He underwent surgery at the beginning of December 1944. It was intended that Cregar's next film would be an adaptation of "Les Misérables" directed by John Brahm, and Billy Rose wanted to star him on Broadway in "Henry VIII". A few days after surgery, Cregar had a heart attack and was rushed to the hospital. He rallied briefly when put in an oxygen tent, but died on December 9, aged 31 years. His mother was at his bedside. "Hangover Square" was released two months after his death.