Testosterone has a complex variety of roles in male physiology. It is a common belief that testosterone in men declines with age. While this is true, there are several aspects to this decline which make it difficult to diagnose definitively, as other endocrine components can contribute to a patient's symptoms. There are some guidelines to help determine when to begin treatment, based on laboratory assays and symptomatology. Testosterone replacement in men can improve overall quality of life, can reverse some of the effects of hypogonadism, and can be done very safely with available pharmacologic agents.