BACKGROUND: Postoperative nausea and vomiting (PONV) is one of the most frequent and distressing side effects of surgery, and approximately 50-70% of patients who undergo gynecologic surgery suffer from PONV. In this study, we evaluated the effects of various doses of ramosetron on postoperative nausea and vomiting following gynecologic surgery. METHODS: This study evaluated a randomized placebo-controlled study comprised of 200 patients who underwent gynecologic surgery under general anesthesia. The patients were divided into the following 4 groups; placebo group (saline 4 ml), R15 group (ramosetron 0.15 mg), R30 group (ramosetron 0.3 mg) and R45 group (ramosetron 0.45 mg). Each patient was administered the study drug intravenously at the completion of the operation and the presence and severity of PONV were then evaluated 24 and 48 hours after the operation. RESULTS: The incidence of PONV during the first 24 hours following surgery was lower in patients in the R30 group (44%) than in patients in the placebo group (68%)(P < 0.05). In addition, the incidence of PONV 24 to 48 hours after the operation was lower in patients in the R30 group (12%) and the R45 group (14%) than in patients in the placebo group (44%)(P < 0.05) Moreover, common side effects of 5-HT3 receptor antagonist such as headache, dizziness, and constipation did not develop in any of the groups. CONCLUSIONS: The results of this study indicate that 0.3 mg of ramosetron is the most effective dose for preventing PONV during to the first 48 hours following gynecologic surgery.