Erectile dysfunction (ED) is a clinical disorder that results from a continuous spectrum of clinical factors, including physical illness (comprising the organic component of ED), reaction to stress (the intrapsychic component of ED) and relationship difficulties (the relationship component of ED). Testosterone clearly has a relevant role in all three causes of ED; the usefulness of this hormone in the treatment of ED has not, however, been completely clarified. The main physiological action of testosterone in the male sexual response is to regulate the timing of the erectile process as a function of sexual desire, thereby coordinating penile erection with sex. The link between ED, hypogonadism and underlying disorders (such as metabolic syndrome and type 2 diabetes mellitus) is nowadays well documented. The recognition of underlying disorders might be useful in motivating men with ED to improve their health-related lifestyle choices. Hence, patients with ED might be considered 'lucky', because their disorder offers the opportunity to undergo medical examinations to detect underlying disease. Both ED and hypogonadism are treatable conditions. A range of testosterone preparations are available for supplementation; their combination with phosphodiesterase 5 inhibitors might improve outcomes in some cases.