 The rationale for investigating the hypothesis that there is an association between erectile dysfunction ED and the subsequent development of prostate cancer is based on three assumptions: 1 baseline ED is common in most if not all of the cross-sectional studies in men with prostate cancer; 2 the development of ED and prostate cancer may have certain shared common risk factors; and 3 the use of testosterone for the treatment of ED has been suspected to be associated with prostate cancer development. Controversy exists over whether men with ED have an increased risk of subsequent prostate cancer. Few studies have evaluated the risk of developing prostate cancer for men with ED. The investigators, therefore, conducted a population-based longitudinal study with eight years follow-up to examine this association and to evaluate the magnitude of the risk. 