Irritable bowel syndrome in office-based practice in the United States. United States estimates of the frequency of visits to physicians and patterns of medical care for the diagnosis of the irritable bowel syndrome were derived from the 1975, 1980-1981, and 1985 National Ambulatory Medical Care Surveys. These surveys of office-based physicians allow national estimates of various aspects of ambulatory care. The overall rate of visits with the diagnosis of irritable bowel syndrome in 1980-1981 and 1985 were 10.6 per thousand U.S. population. Women had 2.4 times the rate of visits by men and rates rose in both sexes until middle-age. Irritable bowel syndrome was the leading digestive disease diagnosis among gastroenterologists but only the seventh leading diagnosis among all physicians. Gastrointestinal symptoms, association with mental disorders, prescriptions, and disposition were also examined in patients with visits for irritable bowel syndrome. Among records with digestive tract symptoms and a first listed diagnosis of irritable bowel syndrome, stomach or abdominal pain was listed on only about one half of records and disorders of bowel function were listed on fewer than 40%. In 1975 and 1985, irritable bowel syndrome was noted approximately twice as often as other digestive diseases at visits with mental disorder symptoms and diagnosis, although mental disorder symptoms and diagnoses were noted at fewer than 15% of visits with irritable bowel syndrome. Medications were prescribed at approximately 75% of visits for irritable bowel syndrome; the most common were gastrointestinal medications followed by combination gastrointestinal-psychoactive medications. Subsequent appointments were scheduled following at least 50% of the visits of patients with irritable bowel syndrome. 