The aims of the Men's Attitudes to Life Events and Sexuality (MALES) study were to identify prevalence of erectile dysfunction (ED) and related health issues in the general male population in Europe, North and South America, and to examine the attitudes and behavior of men in relation to these health issues. Phase I of the MALES study involved 27839 men aged 20-75 years who were interviewed in eight countries (United States, United Kingdom, Germany,France, Italy, Spain, Mexico, and Brazil) using a standardized questionnaire. Phase II of the MALES study involved 2912 men who were recruited from the sub-sample of Phase I MALES participants who reported ED together with additional men with ED recruited from other sources. Prevalence of ED and associated attitudes. The overall prevalence of ED in the MALES sample was 16%. ED prevalence varied markedly by country, however, from a high of 22%of men in the US reporting ED to a low of 10% in Spain. The prevalence of self-reported ED increased with increasing age. Men with co-morbid medical conditions and risk factors, including cardiovascular disease, hypertension, dyslipidemia,and depression all reported higher prevalence of ED. Men with ED also reported increased prevalence rates of these co-morbid conditions. MALES Phase II data indicated that among men who reported ED, 58% had actively sought medical attention for their condition; however, only 16% of men with ED were currently being treated with oral PDE-5 therapy. The MALES study confirms the high prevalence rates of ED and its association with co-morbid medical conditions, such as diabetes and depression, reported in other large-scale, epidemiological studies. Despite the advent of oral phosphodiesterase inhibitors, only 58% of ED sufferers consult a physician about their problem, and only 16% of men with self-reported ED maintain their use of oral therapy.