In September 1974, Sullivan had x-rays done. They showed that Sullivan had esophageal cancer. Only his family was told about it. Because the doctors did not give Sullivan a lot of time, the family chose not to tell him about it. Sullivan thought that his illness was because of ulcers. He died five weeks later, on October 13, 1974, at New York's Lenox Hill Hospital. 3,000 people went to his funeral. It was held at St. Patrick's Cathedral, New York.