A steady decline in androgen levels occurs in males as they age. Evidence suggests that this decline may be at least partially responsible for a variety of physical and mental changes associated with the aging process. For instance, abnormally low levels of androgens can lead to profound changes in bone density, body composition, as well as sexual and cognitive function. Testosterone replacement has been shown to produce improvements in many of these areas. However, this practice is not without risks, both proven and theoretic. Also, the diagnosis of androgen deficiency and the decision to treat is not always straightforward. The purpose of this article is to familiarize the clinician with issues associated with androgen deficiency in the aging male. The clinical symptoms of androgen deficiency as well as the risks and benefits of androgen replacement will be discussed. This should help clinicians better identify those patients in whom testosterone replacement therapy should be considered.