Background: The aim of this study was to determine an intravenous dose of ketorolac providing augmentation of analgesia and lowering adverse events for patients using postoperative intravenous patient-controlled analgesia (IV-PCA) with morphine Methods: One hundred and ninety eight patients who underwent an elective gynecologic operation were allocated to one of seven groups (ketorolac 180 mg K6, ketorolac 150 mg + morphine 10 mg K5M1, ketorolac 120 mg + morphine 20 mg K4M2, ketorolac 90 mg + morphine 30 mg K3M3, ketorolac 60 mg + morphine 40 mg K2M4, ketorolac 30 mg + morphine 50 mg K1M5, morphine 60 mg M6). After a loading dose of 3 ml, the PCA was started at a setting of 1 ml per demand, with a 8 minute lockout interval and 5-h limit. Results: The total PCA volume was lower in the K3M3, K2M4 and M6 groups. Visual analogue scale pain scores were higher in the K6 and M6 groups. More additional analgesics were required in the K6, K5M1, K1M5 and M6 groups. More antiemetics were required in the M6 group, although the incidence of nausea/vomiting and pruritus was similar among the groups. The sedation scores were lower in the K6 group and higher in the M6 group, 6 h postoperatively; and higher in the M6 and K1M5 groups, 24 h postoperatively. Conclusions: The combination of morphine 30 mg and ketorolac 90 mg, or morphine 40 mg and ketorolac 60 mg in IV-PCA with a total volume of 60 ml, is more effective in analgesia and has less adverse events.