The aging of the world population has brought to the forefront of medical practice the diagnosis and treatment of hypogonadism in adult men. There is an increasing interest on the use of testosterone (T) and other androgens to manage men with clinical and biochemical evidence of hypogonadism. Although treatment with T has been used for 70 yr and it is, generally, safe and effective, there are a number of safety issues--ranging from cardiovascular and lipid alterations to hematological changes--that the physician needs to be aware of. Unquestionably, prostate safety constitutes the most important one. No evidence exists that appropriate androgen administration with knowledgeable monitoring carries significant or potentially serious adverse effects on the prostate gland. Men with symptomatic lower urinary obstruction need to be assessed carefully prior to androgen administration. The suspicion of prostate cancer is an absolute contraindication for T use. Recommendations are available for the judicious and safe use of T in aging men.