Vasectomy has been reported to be associated with an increased risk of prostate cancer in western countries. A hospital-based case-control study was conducted in 12 cities in China to evaluate the relationship between vasectomy and prostate cancer risk in China, a low-risk country with rising incidence and increasing use of vasectomy. Interviews were conducted with 138 histologically confirmed prostate cancer cases diagnosed during 1989-1992 and 638 controls (158 hospital cancer, 158 hospital noncancer, and 322 neighborhood controls) of similar ages. Vasectomy at least 10 years prior to interview was reported by 10% of the cases versus 3% of the controls. Odds ratios for prostate cancer associated with vasectomy were 2.0 (95% confidence interval, 0.7-6.1), 3.3 (95% confidence interval, 1.0-11.3), and 6.7 (95% confidence interval, 2.1-21.6), respectively, when hospital cancer, hospital noncancer, and neighborhood controls were used for comparison. Although detection bias is of concern, the data suggest that in China, men with a history of vasectomy may experience an increased risk of prostate cancer.