It has been part of the conventional medical wisdom for six decades that higher testosterone in some way increases the risk of prostate cancer. This belief is derived largely from the well-documented regression of prostate cancer in the face of surgical or pharmacological castration. However, there is an absence of scientific data supporting the concept that higher testosterone levels are associated with an increased risk of prostate cancer. Specifically, no increased risk of prostate cancer was noted in 1) clinical trials of testosterone supplementation, 2) longitudinal population-based studies, or 3) in a high-risk population of hypogonadal men receiving testosterone treatment. Moreover, hypogonadal men have a substantial rate of biopsy-detectable prostate cancer, suggesting that low testosterone has no protective effect against development of prostate cancer. These results argue against an increased risk of prostate cancer with testosterone replacement therapy.