Testosterone supplementation is commonly used as a treatment for hypogonadal men with or without erectile dysfunction. The effect of parenteral testosterone replacement therapy on the development or growth of prostate cancer is unclear. We assessed the effect of this treatment on serum prostate-specific antigen (PSA) levels and risk of prostate cancer in hypogonadal men with erectile dysfunction. Criteria for inclusion were a normal pre-treatment PSA (<4.0 ng/mL) in conjunction with a normal digital rectal examination (DRE) or a negative pretreatment prostate biopsy for men with either an abnormal DRE or an elevated PSA. Patients received intramuscular injections every 2 to 4 weeks, allowing for dose titration. In this retrospective analysis, 54 hypogonadal men with erectile dysfunction were included, with a mean age of 60.4 years (range 42.0-76.0) and a mean follow-up of 30.2 months (range 2.0-82.0) on testosterone therapy. Mean pretreatment total testosterone level was 1.89 ng/mL (range 0.2-2.92), which increased during treatment to a mean of 9.74 ng/mL (range 1.50-26.30, P <.001). Mean pretreatment PSA was 1.86 ng/mL (median 1.01 ng/mL, range 0.0-15.80), which increased to a mean PSA level of 2.82 ng/mL (median 1.56 ng/mL, range 0.0-32.36, P <.01) with testosterone treatment. Of the 54 men included in this study, 6 (11.1%) required prostate biopsy while on testosterone therapy because of a rise in serum PSA above 4.0 ng/mL. One patient (1.9%) was diagnosed with prostate cancer. In conclusion, testosterone replacement therapy in men with erectile dysfunction and hypogonadism is associated with a minor PSA elevation, but there does not appear to be a short-term increase in risk for the development of prostate cancer.