The aim of this study was to conduct a quantitative review of prostate cancer studies to pool relative risk (RR) estimates on the association between prostate cancer and vasectomy, in an attempt to determine whether there is an association, and if so, its magnitude. Random-effects models were examined along with a linear model for time since vasectomy. The pooled RR estimate was 1.37 (95% CI=1.15-1.62) based on five cohort studies and 17 case-control studies. The RR estimate varied by study design with the lowest risk for population-based case-control studies. No difference was seen in risk by age at vasectomy. A linear trend based on the 16 studies reporting time since vasectomy suggested an 10% increase for each additional 10 y or a RR of 1.32 (95% CI=1.17-1.50) for 30 y since vasectomy. When null effects were assumed for the six studies not reporting information, the linear RR for the 22 studies was 1.07 (1.03-1.11) and 1.23 (1.11-1.37) for 10 and 30 y since vasectomy, respectively. These results suggest that men with a prior vasectomy may be at an increased risk of prostate cancer, however, the increase may not be causal since potential bias cannot be discounted. The overall association was small and therefore could be explained by bias. The latency effect shown here for time since vasectomy should be examined further.