Urologists play a significant role in the diagnosis and treatment of male erectile dysfunction (ED). But the context of diagnosing and treating ED has profoundly changed over the past decade, in that it is no longer viewed as an independent entity. Rather it is recognized that in many (but not all) patients, there is a close association with the so called “metabolic syndrome” and on occasions with hypogonadism. In order to treat men with ED appropriately in this context, it is important for the urologist to become familiar with the intricacies of the metabolic syndrome and also with the diagnosis and treatment of male hypogonadism.While understanding of the metabolic syndrome involves the urologist in the understanding the management of hypertension, dyslipidaemia and diabetes, (most of which will be have changed considerably since he first learnt about them at medical school), an understanding of testosterone metabolism is much closer to home. Urologists are trained to use testosterone withdrawal as a treatment for prostate cancer, and it is only a short intellectual step to believing that there is an association between testosterone replacement and the development of prostate cancer. However, while the evidence for the former is considerable, the evidence to support the latter relationship is lacking.There is increasing evidence that there is a role for the responsible treatment of elderly men who are hypogonadal with testosterone while at the same exercising due caution in relation to any potentially harmful effects of testosterone administration on the prostate and the hematopoietic system. To this end a number of sets of guidelines for diagnosing and treating elderly men with testosterone deficiency have been developed.