For a case-control study of risk factors for renal cell carcinoma, a mailed questionnaire was used to collect data on 518 cases and 1,381 population-based controls in Ontario, Canada. Active cigarette smoking increased risk twofold among males (odds ratio estimate [OR] = 2.0, 95 percent confidence interval (CI) = 1.4-2.8) and females (OR = 1.9, CI = 1.3-2.6). Passive smoking appeared to increase risk somewhat among nonsmokers (males: OR = 1.6, CI = 0.5-4.7; females: OR = 1.7, CI = 0.8-3.4). A high Quetelet index (QI) was associated with a twofold increase in risk in both sexes, although this was based on reported weight at age 25 years for males (OR = 1.9, CI = 1.2-3.1) and five years prior to data collection for females (OR = 2.5, CI = 1.4-4.6). Diuretic use was associated with significantly increased risk among females, but not among males. Phenacetin use increased risk, while acetaminophen use was not associated with altered risk, although few subjects used either compound. Multiple urinary tract infections increased risk, but only significantly in females (OR = 1.9, CI = 1.2-2.9). Our data indicate the need for further exploration of passive smoking and diuretics as risk factors, as well as elucidation of mechanisms by which high lifetime QI and frequent urinary-tract infections might increase risk of this cancer.