Recent incidence data from the United States indicate that transitional cell carcinoma accounts for the vast majority (95%) of bladder tumors in this country, with squamous cell carcinoma (less than 3%) and adenocarcinoma (less than 2%) comprising nearly all the remaining cases. Rates of squamous cell carcinoma and adenocarcinoma were higher in blacks compared to whites, while the reverse was true for transitional cell carcinoma. All three tumors predominated in males, especially transitional cell carcinoma. A population-based case-control study of bladder cancer conducted in 10 geographical areas of the United States identified 43 patients with squamous cell carcinoma and 32 with adenocarcinoma to permit an examination of risk factors. Cigarette smoking was significantly associated with risk of squamous cell carcinoma, with the relative risk rising to 6.1 among smokers of 40 or more cigarettes/day. Significantly elevated risks of squamous cell carcinoma were also associated with a history of 3 or more urinary tract infections (relative risk = 5.7) and with employment as welders and cooks. Risk factors were generally less conspicuous for adenocarcinoma, except for a significant trend with the amount of coffee drinking; however, this finding is based on small numbers and should be interpreted cautiously.