Functional gastrointestinal disorders, including the irritable bowel syndrome, account for up to 40% of referrals to gastroenterologists, but accurate data on the natural history of these disorders in the general population are lacking. Using a reliable and valid questionnaire, the authors estimated the onset and disappearance of symptoms consistent with functional gastrointestinal disorders. An age- and sex-strattfied random sample of 1,021 eligible residents of Olmsted County, Minnesota, aged 30–64 years were initially mailed the questionnaire; 82% responded (n = 835). In a remailing to responders 12–20 months later, 83% responded again (n = 690). The age- and sex-adjusted prevalence rates per 100 for irritable bowel syndrome, chronic constipation, chronic diarrhea, and frequent dyspepsia were 18.1 (95% confidence interval (Cl) 15.1–21.1), 14.7 (95% Cl 11.9–17.4), 7.3 (95% Cl 5.3–9.3), and 14.1 (95% Cl 11.5–16.8), respectively, on the second mailing. Symptoms were not significantly associated with nonresponse to the second mailing; moreover, the estimated prevalence rates were not significantly different from the first mailing. Among the 582 subjects free of the irritable bowel syndrome on the first survey, 9% developed symptoms during 795 person-years of follow-up, while 38% of the 108 who initially had the irritable bowel syndrome did not meet the criteria after 146 person-years of follow-up. Similar onset and disappearance rates were observed for the other main symptom categories. While functional gastrointestinal symptoms are common in middle-aged persons and overall prevalence appears relatively stable over 12–20 months, substantial turnover is implied by the observed onset and disappearance rates; several potential sources of bias do not seem to account for this variation. Am J Epidemiol 1992;136:165–77.