Testosterone replacement therapy is often equated with the macho male physique and virility and is viewed by some as an antiaging tonic. The growth in testosterone's reputation and its increased use by men of all ages has seemed to outpace the scientific evidences. This review will aim to examine the uncertainty regarding the nature and the clinical importance of the age-related reduction in the testosterone levels. Considerations will be given both to clinical symptoms, biochemical and clinical diagnostic criteria, and to the risk-to-benefit ratio of reversing late-onset hypogonadism in aging and older men.