To investigate the frequency of cigarette smoking in patients who have been diagnosed with bladder cancer, data were obtained for 1507 subjects listed in the 1975 private census of Washington County, Maryland. Case subjects were defined as persons at least 18 years of age diagnosed with bladder cancer (ICD code = 188.0 to 188.9) between 1975 and 1992 for whom smoking information was available. Control subjects were defined as a random sample of persons frequency matched by age and sex to the cases. Controls were free of bladder cancer and had smoking information available. The odds ratio for current smokers for the association between smoking and bladder cancer adjusted for age and sex was statistically significant (OR = 1.68, 95% confidence intervals, 1.22 to 2.32). The chi-square trend test of the dose-response results was significant (chi-square = 11.69, df = 1, P < .01).