BACKGROUND: Postoperative nausea and vomiting (PONV) is a common problem in patients undergoing thyroidectomy. In this study we evaluated the effects of prophylactic dolasetron and/or induction with propofol on PONV. METHODS: Two hundred three patients scheduled thyroidectomy under general anesthesia with sevoflurane were included and were randomly allocated to one of four groups. In control (group C) and dolasetron groups (group D), the patients received thiopental sodium 4-5 mg/kg intravenously for the induction of anesthesia, and the patients in group D received prophylactic intravenous dolasetron 210 microgram/kg. In propofol (group P) and dolasetron + propofol groups (group D + P), the patients received propofol 2 mg/kg intravenously for the induction of anesthesia, and the patients in group D + P received prophylactic intravenous dolasetron 210 microgram/kg. The incidence and severity of PONV, the need for rescue antiemetics, adverse events were assessed during 0 to 1 hour and 1 to 24 hours postoperatively. RESULTS: During the first 24 hours after anesthesia, the incidences of PONV and postoperative vomiting were significantly reduced in group D + P compared with group C (P < 0.05, respectively). There were no significant differences in postoperative nausea, need for rescue antiemetics, severity of PONV, and adverse events of antiemetics among the four groups. CONCLUSIONS: In patients with thyroidectomy, combination of prophylactic dolasetron administration and induction with propofol was found to reduce the incidence of PONV during the first 24 hours after anesthesia, compared with that of routine induction with thiopental sodium.