Several studies suggest that tubal sterilization may decrease the risk of ovarian cancer. Data from the Cancer Prevention Study II were analyzed to examine the relation between tubal ligation and ovarian cancer mortality in a large prospective study. A total of 396,114 women who had not had hysterectomies and who had no prior history of cancer (except nonmelanoma skin cancer) were followed prospectively for approximately 9 years from 1982 to 1991. During this time, 799 ovarian cancer deaths were observed. Tubal ligation was significantly associated with a decreased risk of ovarian cancer mortality in an age- and race-adjusted Cox proportional hazards model (hazard ratio (HR) = 0.64, 95% confidence interval (CI) 0.42-0.96), and the results were essentially unchanged when controlling for potential ovarian cancer risk factors (HR = 0.68, 95% CI 0.45-1.03). The protective effect appeared to be greater in the first 20 years after the procedure (HR = 0.49, 95% CI 0.24-0.99) than later (HR = 0.80, 95% CI 0.48-1.34). No interactions between ever having had a tubal ligation and other covariates were observed. These data suggest that tubal ligation reduces the risk of fatal ovarian cancer.