Data from six large, systematic national health surveys were examined to provide a more complete description of the epidemiology of irritable bowel syndrome in the United States. Data from the Second National Health and Nutrition Examination Survey, 1976-1980, indicated 4.7 million people (2.9% of the population) with self-reported diagnoses of irritable bowel syndrome. Rates for women were 3.2 times those for men, and rates for whites were 5.3 times those for blacks. Rates were highest among those aged 45-64 years. More than 2.6 million (1.6% of the population) were symptomatic at the time of the survey. Data from the National Ambulatory Medical Care Survey, 1985, and the National Disease and Therapeutic Index, 1987, documented between 2.4 and 3.5 million yearly visits to physicians by patients with irritable bowel syndrome and more than 2.2 million medications prescribed. Rates of hospitalization for women have fallen from 71.9 (per 100,000 population) in 1982 to 21.1 in 1987 based on data from the National Hospital Discharge Survey. A similar pattern was observed in data from the Commission on Professional and Hospital Activities. The data support the impression that irritable bowel syndrome is a prevalent condition in the United States with significant impact on health care. Large-scale, population-based surveys using standard criteria are needed to estimate the true extent of irritable bowel syndrome.