By far, the largest known preventable cause of cancer is cigarette smoking. The percentage of cancer deaths in Korea due to tobacco is still increasing. Smoking cigarette at an early age has become more common among women. Tobacco consumption is related causally to cancer to the lung, mouth, larynx, esophagus, bladder, kidney, uterine cervix, and pancreas. Recently, several studies demonstrated that there is very strong correlation between cigarette smoking and p53 mutations in lung cancer, head and neck cancer, and bladder cancer. The recent findings of cigarette smoking and cancer, p53 and bcl-2 mutations, adverse effects of smoking on the effects of radiotherapy, and benefits of quitting will be discussed.