This randomized, double-blinded, placebo-controlled study was conducted to evaluate the effect of orally preoperative 600 mg of gabapentin on postoperative pain control in patients undergoing total hip replacement. Patients were randomly divided into 2 groups according to the drug used before surgery: group I (n = 30, placebo) and group II (n = 30,600 mg of gabapentin). Patient controlled analgesia by morphine was used to reduce postoperative pain in 2 groups. The visual analog scale (VAS) score, morphine consumption and adverse effects were recorded during 48 hours postoperatively. There were no significant difference in the patient, anesthesia and surgery related characteristics between 2 groups (p 0.05). The mean VAS scores at rest were significantly lower in group II than in group I (p 0.05), but mean VAS scores on movement were comparable. The median time to first analgesic was significantly longer (176.3 +/- 29.0 vs 194.6 +/- 22.5 min, p 0.05) in the gabapentin group than in the placebo group. The consumption of morphine in the first day was lower in group II (28.2 +/- 10.6 vs 34.5 +/- 12.6 mg, p 0.05), but there is no difference between 2 groups on the second day (67.7 +/- 21.3 vs 58.6 +/- 22.5 mg, p 0.05). The incidences of side effects were similar in 2 groups. Conclusions: preoperative 600 mg gabapentin decreased pain scores and morphine consumption in the first 24 hours after total hip replacement without affecting the morphine related adverse effects.