This paper: (i) describes the worldwide prevalence of erectile dysfunction (ED); (ii) presents age-specific incidence rates for ED in the US; (iii) summarizes some key epidemiologic correlates of ED in the general population; and (iv) considers the possibility that ED may be a biobehavioral marker (sentinel event) of subsequent cardiovascular disease in men. Clinical, anthropometric, life style and hormonal data are presented from the milestone Massachusetts Male Aging Study (MMAS), a large (over 1000) prospective cohort of randomly sampled community-dwelling, normally aging men. Newly updated population prevalence and (more importantly) age-specific incidence rates are reported. We also estimate the likely magnitude of ED that will accompany the worldwide globalization of aging. Key correlates (predictors) of incident ED, especially vasculogenic influences, are identified and discussed. In conclusion, ED is a common biobehavioral phenomenon and there are strong physiological and epidemiological reasons for considering it a major marker (or predictor) of subsequent cardiovascular disease in men. International Journal of Impotence Research (2000) 12, Suppl 4, S6-S11.