Patients with prostate cancer can present with hypogonadism and experience health and quality-of-life declines related to low testosterone levels. Despite generations of urological dogma suggesting that testosterone supplementation therapy (TST) for hypogonadism causes prostate-cancer progression, a review of the contemporary literature provides evidence to the contrary. The prostate saturation model suggests that the androgen receptor (AR) is saturated at serum testosterone levels of 150-200 ng/dl, and that additional serum testosterone above this level has limited, if any, effects within the prostate. Indeed, studies in the modern era of PSA assessments indicate that TST does not affect prostate size, intraprostatic testosterone levels, or prostate-cancer progression, provided the baseline serum testosterone level is greater than this AR saturation point. However, the body of data on this subject comes from a small number of cases, and TST should only be administered to patients with prostate cancer after thorough discussions of the risks and benefits, with subsequent careful monitoring.