Introduction. This is a report of a population-based cross-sectional observational study in Western Australia (WA) on male erectile dysfunction (ED).Aim. To assess the prevalence of ED in WA and to examine its associated sociodemographic factors.Method. Postal questionnaires were sent to randomly selected age-stratified male population samples obtained from the WA Electoral Roll.Main Outcome Measures. In addition to items covering sociodemographic and clinical information, the Australian Standard Classification of Occupations (ASCO), the Socioeconomic Index for Area (SEIFA), and the 5-item International Index of Erectile Function (IIEF-5) were used.Results. One thousand seven hundred seventy (41.9%) of 4,228 questionnaires were returned. One thousand five hundred eighty (89.3%) were completed questionnaires from men aged 20.1 to 99.6 years (mean 57.9, median 59.1, standard deviation 18.5). The prevalences of any ED and of severe ED among adult males in WA, adjusted for age distribution, were 25.1 and 8.5%, respectively. Standardized to World Health Organization (WHO) World Standard Population, the corresponding prevalences were 23.4 and 7.4%. Prevalence, as well as severity, of ED increased with age. Thirty-eight percent of the participants who were married or had partners experienced ED (severe ED 19.1%). The prevalence of ED was not significantly different between "white-collar" and "blue-collar" workers. Despite the great majority of the affected participants having experienced ED for > 1 year, only 14.1% reported having ever received any treatment for ED.Conclusions. The study has provided population-based epidemiological data on ED in Western Australian men covering a wide range of ages. The finding that ED is age related, highly prevalent, and grossly underdiagnosed and undertreated is pertinent to global population aging and a rapidly aging Australian population. To facilitate comparisons across populations with different age distributions, all future population-based studies on ED should be standardized to WHO World Standard Population.