Walt Disney had been a heavy smoker since World War I. He did not use cigarettes with filters, and had smoked a pipe as a young man. In November 1966, he was diagnosed with lung cancer and was treated with cobalt therapy. On November 30 he felt unwell and was taken to St. Joseph Hospital where, on December 15, ten days after his 65th birthday, he died of circulatory collapse caused by lung cancer.
Source: Wikipedia