Erectile dysfunction (formerly known as impotence) is defined as the consistent inability to achieve or maintain an erection suitable for intercourse. Until recently, most of the information on the prevalence of erectile dysfunction has been based on small studies of selected population samples. More reliable data became available with the completion of the Massachusetts Male Aging Study. Data from this study indicate that erectile dysfunction is a common condition with an estimated incidence rate of 26 cases per 1000 man-years. In 1993, the National Institutes of Health Consensus Conference estimated that 10 to 20 million men in the USA have problems with erection.