The purpose of the present randomized, double blind placebo controlled study was to compare the effect of ondansetron, a 5 HT 3 subtype of serotonin receptor antagonist, with placebo, in preventing postoperative nausea and vomiting. A total of forty-nine patients undergoing total abdominal hysterectomy were assigned to the study. The patients received either 4 mg intravenous ondansetron or a matching placebo, prior to induction of anesthesia. The number of episodes of emesis and nausea were recorded at 1 hour, 4 hour and 8 hour after recovery from anesthesia. The nausea and womiting scores at 1h 4h and 8h in the ondansetron group were significantly lower than the placebo group (p<0.05). The incidence of the most frequently occuring side effects in the ondansetron group were headache in 15.38 % and dizziness in 7.7 % of the patients. In conclusion, ondansetron appears to be an effective agent in the prophylaxis of postoperative nausea and vomiting in gynecologic operations.