"If I'd carried on smoking, I'd probably have died from a smoking-related illness, and I think that's really bad," she told the U.K.'s The Daily Mirror.
The 27-year-old singer also said she gave up smoking because cancer runs in her family. Her father, Marc Evans, 53, was previously diagnosed with bowel cancer.
Adele admitted to smoking on average 25 cigarettes daily. In fact, her habit caused her to lose her voice in 2011 and cancel shows. After an operation, the "Hello" singer said doctors told her that if she didn't quit she could do permanent damage to her voice.