Background: Three decades after US and Australian forces withdrew from Vietnam, there has been much public interest in the health consequences of service in Vietnam. One controversial question is whether the risk of prostate cancer amongst Vietnam veterans is increased. This paper examines relationships between military history, family history and risk of prostate cancer in a population-based case control study.Methods: Cases were selected from the Cancer Registry of Western Australia as incident cases of histologically-confirmed prostate cancer, and controls were age-matched and selected from the Western Australian electoral roll. Study participants were asked to report any military service history and details about that service.Results: Between January 2001 and September 2002, 606 cases and 471 controls aged between 40 - 75 years were recruited. An increased prostate cancer risk was observed in men reporting they were deployed in Vietnam although this was not statistically significant ( OR = 2.12; 95% CI 0.88 - 5.06). An increased risk was also observed in men reporting prostate cancer in fathers ( OR = 1.90; 95% CI 1.20 - 3.00) or brothers ( OR = 2.05; 95% CI 1.20 - 3.50) diagnosed with prostate cancer.Conclusion: These findings support a positive association between prostate cancer and military service history in the Vietnam war and a first degree relative family history of prostate cancer.