This prospective, randomized, placebo-controlled, double-blinded study was designed to evaluate the efficacy of tropisetron in preventing postoperative nausea and vomiting after elective supratentorial craniotomy in adult patients. We studied 65 ASA physical status I-III patients aged 18 to 76 years who were undergoing elective craniotomy for resection of various supratentorial tumors. Patients were divided into two groups and received either 2 mg of tropisetron (group T) or saline placebo (group P) intravenously at the time of dural closure. A standard general anesthetic technique was used. Episodes of nausea and vomiting and the need for rescue antiemetic medication were recorded during 24 hours postoperatively. Demographic data, duration of surgery and anesthesia, and sedation scores were comparable in both groups. Nausea occurred in 30% of group T patients and in 46.7% of group P patients (P > .05). The incidence of emetic episodes was 26.7% and 56.7% in the two groups (P < .05). Rescue antiemetic medication was needed in 26.7% and 60% of the patients (P < .05). Administration of a single dose of tropisetron (2 mg intravenously) given at the time of dural closure was effective in reducing postoperative nausea and vomiting after elective craniotomy for supratentorial tumor resection in adult patients.