The incidence and precipitating factors associated with symptomatic gastroesophageal reflux were evaluated by a questionnaire in 446 hospitalized and 558 nonhospitalized subjects. Of 385 control subjects 7% experienced heartburn daily, 14% noted heartburn weekly, and 15% experienced it once a month, giving a total of 36% of subjects having heartburn at least monthly. Daily heartburn occurred at a significantly greater (P less than 0.05) rate for 246 medical inpatients (14%) and for 121 patients seen in outpatient gastroenterological clinic (15%). Pregnant women seen in uncomplicated obstetrical clinic had symptoms of significantly greater (P less than 0.01) incidence: daily (25%) and at least once monthly (52%). Age, sex, or hospitalization did not significantly affect incidence. Fried foods, "spicy" foods, and alcohol were the most common precipitating factors.