Active cigarette smoking is a major risk factor for bladder cancer. Secondhand exposure to cigarette smoke may also contribute to bladder carcinogenesis. The authors conducted a prospective cohort study to examine the influence of both active smoking and household exposure to secondhand smoke (SHS) on subsequent bladder cancer risk. The study population included persons from two cohorts established from private censuses conducted in Washington County, Maryland, in 1963 (n = 45,749; 93 cases) and 1975 (n = 48,172; 172 cases). Poisson regression models were fitted to estimate the relative risk of bladder cancer associated with active and passive smoke exposure in the two cohorts (referent category: never smokers who did not live with any smokers). Current smokers had an elevated risk of bladder cancer in both the 1963 cohort (relative risk (RR) = 2.7, 95% confidence limits (CL): 1.6, 4.7) and the 1975 cohort (RR = 2.6, 95% CL: 1.7, 3.9) after adjustment for age, education, and marital status. Among nonsmoking women, current household SHS exposure was associated with bladder cancer risk in the 1963 cohort (RR = 2.3, 95% CL: 1.0, 5.4) but not in the 1975 cohort (RR = 0.9, 95% CL: 0.4, 2.3). This study further solidifies the evidence that active smoking is causally associated with bladder cancer. Additional studies are needed to determine whether passive smoking is a risk factor for bladder cancer.