Background: Both clinical and experimental studies suggest that gabapentin (GBP) has analgesic effects in neuropathic pain. The aim of the study was to investigate the effect of gabapentin on postoperative pain. Methods: This study was performed on 45 (ASA I-II) patients planned for major orthopaedic surgery. 45 patients were randomized into three equal groups. Patients received 1200 mg GBP (Group I), 800 mg GBP (Group II) or placebo (Group III) 1 h before surgery. Anaesthesia was standardized for all patients. Morphine by intravenous patient-controlled analgesia was applied as 1 mg bolus dose and 7 min lockout time for postoperative analgesia. The pain was evaluated at the first 2 and 4 h after operation. The amount of morphine used was recorded at the same hours. Results: In all groups, there were no significant differences in the demographic characteristics, duration of surgery and anaesthesia, or dose of fentanyl received in the operating room. Pain scores and side effects were similar in all groups. Morphine consumption was lower in the Groups I and II than in the Group III at 2 h and 4 h postoperatively (p < 0.05). Morphine consumption was lower in the Group I than in the Group II at 2 h and 4 h (p < 0.05). Conclusion: Our results demonstrate that a single dose of 1200 or 800 mg oral gabapentin reduces morphine consumption in the early postoperative period. However, gabapentin 1200 mg is more effective than gabapentin 800 mg for pre-emptive analgesic effect. © 2005 VSP.