An epidemiological study was undertaken to provide the first reported estimate of the point prevalence of chronic fatigue syndrome in an Australian community. After a pilot study in a separate location, the population of the Richmond Valley, New South Wales, was sampled using a structured case-finding technique, which included notification from local medical practitioners, the use of a screening questionnaire and standardised interviews conducted by a physician and psychiatrist. In addition, investigations were performed to exclude alternative diagnoses and to assess cell-mediated immunity. Forty-two patients with chronic fatigue syndrome, with a female:male ratio of 1.3:1.0, were detected in a population of 114,000. The mean age at onset of symptoms was 28.6 years (SD, 12.3 years), and the median duration of symptoms from onset to sampling date was 30 months. The social status of the patients was distributed in accordance with that of the remainder of the population sampled, with no bias towards the middle or upper social classes. The disorder was causing considerable incapacity, with 43% of patients unable to attend school or work. The conservative estimate from this study suggests a prevalence on June 30 1988 of 37.1 cases per 100,000 (95% confidence interval [CI], 26.8-50.2). Chronic fatigue syndrome is an important disorder in this Australian community that affects young individuals from all social classes and causes considerable ill health and disability.