Experts’ summary: In the September issue of the Journal of Clinical Oncology, Jacobs and colleagues  report on the association between vasectomy and prostate cancer incidence and mortality. Data from the Cancer Prevention Study Cohort II (1982–2012) was retrospectively analyzed. In this cohort, men aged between 40 yr and 90 yr of age without a previous history of prostate cancer were included. A total of 66 542 men were included to determine the association between vasectomy and prostate cancer incidence, and 363 726 men were included for prostate cancer mortality. Vasectomy status was determined primarily by matched questionnaires from participants’ wives. Prostate cancer was identified by biennial follow-up questionnaires and was verified using both medical records and state cancer registries. Association between vasectomy and prostate cancer incidence and mortality was controlled for by age, race, education, body mass index, smoking, and history of prostatespecific antigen testing. There was no difference in the incidence of prostate cancer in men who had undergone a vasectomy compared with those who did not have a vasectomy (hazard ratio [HR]: 1.02, confidence interval [CI]: 0.96–1.08). In this cohort, there was no association between vasectomy and risk of developing aggressive (HR: 0.95, CI: 0.84–1.08) prostate cancer. Men who had undergone a vasectomy were at an increased risk for nonaggressive prostate cancer (HR: 1.08, CI 1.01–1.15). This study did not find an increased risk between having a vasectomy and dying from prostate cancer (HR: 1.01, CI: 0.93–1.10).