The prevalence and the severity of erectile dysfunction (ED) increase with advancing age; different pathogenetic factors could contribute to age-related ED. We studied organic, relational and intrapsychic components of ED as a function of patients' age in a consecutive series of 977 patients with ED, using the specifically designed structured interview SIEDY. A complete physical examination and a series of biochemical, hormonal, psychometric and penile vascular tests were also performed. Relational factors seems to be more relevant in patients aged over 60 y, while intrapsychic disturbances play a major role in younger subjects. Organic factors are the most important determinant of ED in all age groups, but their contribution is more important in older patients. In fact, basal and dynamic peak cavernosal velocity at Doppler ultrasound penile examination was reduced in older patients. Among hormonal factors, the body mass index-dependent reduction of testosterone in older patients does not seem to play a crucial role in the pathogenesis of ED. No significant correlation was observed between testosterone level and the severity of ED, although patients reporting hypoactive sexual desire showed significantly lower testosterone levels when compared with the rest of the sample. A better understanding of the relative contribution of age-related pathogenetic factors of ED could be of help in the design of appropriate therapeutic approaches.