Context: Vasectomy is a common method of contraception, but concern exists about a reported association with risk of prostate cancer.

Objective: To examine whether vasectomy increases risk of prostate cancer.

Design, setting, and participants: National population-based case-control study of 923 new cases of prostate cancer among men aged 40 to 74 years from the New Zealand Cancer Registry who were on the general electoral roll. Controls (n = 1224) were randomly selected from the general electoral roll, with frequency matching to cases in 5-year age groups. Cases (3-15 months after diagnosis) and controls were interviewed by telephone between January 1997 and November 1999.

Main outcome measures: Relative risk (RR) of prostate cancer for men who had had a vasectomy vs those who had not.

Results: There was no association between prostate cancer and vasectomy (RR, 0.92; 95% confidence interval [CI], 0.75-1.14) nor with time since vasectomy (RR, 0.92; 95% CI, 0.68-1.23 for > or = 25 years since vasectomy). Adjustment for social class, geographic region, religious affiliation, and a family history of prostate cancer did not affect these RRs.

Conclusions: Vasectomy does not increase the risk of prostate cancer, even after 25 years or more.