The primary risk factor for bladder cancer is cigarette smoking. Using a combined analysis of 11 case-control studies, we have accurately measured the relationship between cigarette smoking and bladder cancer in men. Available smoking information on 2,600 male bladder cancer cases and 5,524 male controls included duration of smoking habit, number of cigarettes smoked per day and time since cessation of smoking habit for ex-smokers. There was a linear increasing risk of bladder cancer with increasing duration of smoking, ranging from an odds ratio (OR) of 1.96 after 20 years of smoking (95% confidence interval [CI] 1.48 -2.61) to 5.57 after 60 years (CI 4.18 -7.44). A dose relationship was observed between number of cigarettes smoked per day and bladder cancer up to a threshold limit of 15-20 cigarettes per day, OR ؍ 4.50 (CI 3.81-5.33), after which no increased risk was observed. An immediate decrease in risk of bladder cancer was observed for those who gave up smoking. This decrease was over 30% after 1-4 years, OR ؍ 0.65 (0.53-0.79), and was over 60% after 25 years of cessation, OR ؍ 0.37 (0.30 -0.45). However, even after 25 years, the decrease in risk did not reach the level of the never-smokers, OR ؍ 0.20. (0.17-0.24). The proportion of bladder cancer cases attributable to ever-smoking was 0.66 (0.61-0.70) for all men and 0.73 (0.66 -0.79) for men younger than 60. These estimates are higher than previously calculated. Int.