Changes in understanding regarding the relationship of androgens and prostate cancer have led to changes in the use of testosterone therapy. The evidence supports a finite ability of androgens to stimulate prostate cancer growth, with a maximum achieved at low testosterone concentrations, called the saturation model. The saturation point corresponds with maximal androgenic stimulation at 250 ng/dL. Evidence is reviewed herein regarding the relationship of testosterone to prostate cancer and the relatively new practice of offering testosterone therapy to men with a history of prostate cancer. Although no prospective controlled trials have been performed, results have been reassuring.