BACKGROUND: Postoperative nausea and vomiting are common postoperative complaints. The purpose of this study was to assess the effect of preoperative midazolam on vomiting after appendectomy. METHODS: Sixty patients, aged 10 64 yr, undergoing emergency appendectomy were randomly allocated to receive midazolam 30, 50, 75 microgram/kg or placebo after induction of anesthesia. Anesthesia consisted of 67% nitrous oxide, 33% oxygen and propofol infusion 6 10 mg/kg/h. Postoperative vomiting was checked by the recovery room nurse at 1 h after operation and we examined the incidence of postoperative vomiting at 24 h after operation. RESULTS: Midazolam reduced the overall incidence of vomiting, especially in the midazolam 50 and 75 microgram/kg groups, completely abolishing vomiting (P< 0.05). However, in the midazolam 75 microgram/kg group, there was a delay in eye opening time (P< 0.05). CONCLUSIONS: Preoperative injections of midazolam 30 or 50 microgram/kg were useful to prevent postoperative vomiting in patients undergoing appendectomy without delayed recovery.