We evaluated cigarette smoking as a risk factor for prostate cancer in a prospective, population-based cohortstudy. The subjects were 14,450 males among the participants in the Seoul Male Cancer Cohort Study who hadat least 1-year follow-up. They were followed up between 1993 and 2008. During the 16-year follow-up period,87 cases of prostate cancer occurred over the 207,326 person-years of the study. The age-adjusted relative risksof past and current smokers at entry were 0.60 (95%CI: 0.34-1.06) and 0.70 (95%CI: 0.43-1.13), respectively,suggesting that cigarette smoking may not be a risk factor for prostate cancer. The relationship between prostatecancer and other modifiable factors, such as Westernized diet, should be studied with the goal of establishingprevention programs for prostate cancer.