As an N-methyl-D-aspartate antagonist, magnesium sulfate has analgesic properties and reduces noxious input during surgery. The aim of the study was to determine the effect of preemptive intravenous low-dose magnesium sulfate on early postoperative pain after laparoscopic cholecystectomy. In this prospective, randomized study, 60 ASA I-II patients undergoing elective laparoscopic cholecystectomy were assigned to three groups (n = 20 each). After anesthesia induction, prior to surgical incision, patients received magnesium sulfate 5.0 mg/kg (group A), magnesium sulfate 7.5 mg/kg (group B) or saline intravenously (group C). General anesthesia was performed with the same drugs in all three groups. Postoperative pain intensities at rest, according to the visual analog scale (VAS 0-10), were evaluated at 1, 3, 6, 9 and 24 hours after surgery. According to the VAS scores, patients intravenously received metamizol 2.5 g (VAS 3-4), diclofenac 75 mg (VAS 5-7) or tramadol 1 mg/kg (VAS 8-10). VAS scores at 1 hour postoperatively were significantly lower in groups A (4.7 +/- 1.7; p < 0.05) and B (3.2 +/- 1.8; p < 0.01) than in group C (5.2 +/- 2.0). At 3 hours postoperatively, VAS score was significantly lower in group B (2.4 +/- 1.5) than in group A (3.7 +/- 1.8) or group C (3.8 +/- 2.3) (p < 0.05). After 6, 9 and 24 hours postoperatively, there were no differences in VAS scores among the groups. In conclusion, preemptive intravenous administration of both 5.0 mg/kg and 7.5 mg/kg of magnesium sulfate significantly reduced early postoperative pain after laparoscopic cholecystectomy, but 7.5 mg/kg was found to be more effective. There was no effect on pain reduction at 6, 9 and 24 hours after surgery and no adverse effects were recorded.