Late onset hypogonadism was originally perceived as an academic topic. In the course of two decades it has become an issue impacting on everyday urology. For long time clinical conditions, such as cardiovascular disease, diabetes mellitus type 2, sexual dysfunction and urological complaints affecting the aging male, were regarded as independent clinical entities, treated by a number of medical specialists. Over the last decade their close interrelationship could be convincingly demonstrated. Declining testosterone levels in elderly appear to be central to the above pathologies. Epidemiological studies show that prostate disease occurs at an age when serum testosterone levels decline. It is now clear that erectile dysfunction is a local expression of endothelial dysfunction of the cardiovascular system. Testosterone deficiency is associated with an increased incidence of cardiovascular disease and diabetes mellitus, sequels of the metabolic syndrome. There is a relationship between the metabolic syndrome and lower urinary tract symptoms (LUTS). The pathophysiology of LUTS has much in common with the pathological substrate of erectile dysfunction with regard to vascular factors and the role of nitric oxide, explaining why phosphodiesterase type 5 inhibitors have often a beneficial effect on LUTS. It must be regarded an omission not to include testosterone measurements in the work-up of the LUTS, erectile dysfunction, cardiovascular disease and diabetes mellitus type 2. These conditions hinge on testosterone deficiency, and if testosterone deficiency can be proven, testosterone treatment can improve these conditions. There are many sites in the lower urinary tract where testosterone exerts effects.