Most studies of postoperative nausea and vomiting have concentrated on single etiologic factors and have not detailed the method of assessing these symptoms. This study used postoperative interview data from patients at four teaching hospitals during 1988-89, to determine 1) risk factors for nausea/vomiting, 2) whether the type of surgery affected the rate of nausea/vomiting among female patients, 3) whether differences in rates across hospitals were due to differences in patient case-mix, and 4) whether there were differences in the rate of nausea/vomiting among the patients of individual anesthesiologists. Research nurses performed 16,000 interviews (59% of all inpatients) from a closed-question standardized format. With a multiple logistic regression that controlled simultaneously for all risk factors, factors associated with increased risk for nausea/vomiting for all patients included younger age, female, lower physical status score, no preoperative medical conditions, nonsmokers, elective procedures, longer duration of anesthesia, inhaled anesthetics, use of intraoperative opioids, and gynecologic or ophthalmologic operations. Among women, risk factors were similar, with minor gynecologic surgery associated with increased risk (relative odds = 2.30). We found marked variations in the rate of nausea/vomiting across hospitals (range, 39% to 73%), and these variations were not explained by the case-mix of patients. The rate of nausea/vomiting varied substantially across anesthesiologists in each hospital and the differences were not explained by differences in the patients they managed. Thus in the time period immediately preceding the introduction of newer antiemetic drugs, we found that the rates of this common problem were persistently high as perceived from the patients' point of view.