Background: Preemptive analgesia may decrease postoperative pain by preventing nociceptive inputs generated during surgery. The preemptive effect of intravenous nalbuphine was examined in gynecological surgery. Methods: Forty female patients scheduled for gynecological surgery were randomly allocated into two groups. Each patient received 10 mg of intravenous nalbuphine as a bolus dose at the closure of peritoneum in group I (n=20) and before the skin incision in group II (n=20). After the bolus dose, the intravenous patient controlled analgesia (IV-PCA) which contained 50 mg of nalbuphine, 120 mg of ketorolac, 0.25 mg of droperidol and 90 ml of 5% dextrose water was given continuously at the rate of 2 ml/min. The postoperative visual analogue scale pain score (VAS), the total amount of the analgesics used, the degree of satisfaction of the patients and the developement of side effects were examined for 2 days. Results: VAS were significantly lower in group II than in group I after 9 and 12 hours. The cumulative consumption of analgesics in group II was significantly less than in group I. Most patients were satisfied with this regimen. There were no remarkable side effects. Conclusions: Preemptive analgesia with intravenous nalbuphine decreased postoperative pain and analgesic requirement. The analgesic effect of IV-PCA with nalbuphine-ketorolac was effective in control of postoperative pain in gynecologic surgery.