Although cigarette smoking is a principal risk factor for bladder cancer in both men and women, few studies have statistically evaluated whether gender modifies the effect of smoking on bladder cancer risk. We initiated the present case-control study at Roswell Park Cancer Institute in Buffalo, New York, U.S., to provide further data on this important issue. We observed similar risk estimates for men and women with comparable smoking exposures, but did not observe a statistically significant interaction between gender and lifetime smoking exposure. We conclude that cigarette smoking is a major risk factor for bladder cancer in both sexes, but that gender does not modify the effect of smoking on bladder cancer risk.