Postoperative pain is one of the most troublesome aspects of tonsillectomy for patients. Although various analgesics have been administered for pain control following tonsillectomy, it has still not been effectively controlled. Therefore, this study was conducted to evaluate the effectiveness of premedication using gabapentin on postoperative pain control in patients undergoing tonsillectomy. A total of 58 adult patients were randomly divided into a control group and a gabapentin group. Patients in the control group received an oral placebo preoperatively, whereas those in the gabapentin group received an oral dose of gabapentin preoperatively. All participants were provided with patient-controlled analgesia using fentanyl for 48 h after surgery. The total amount of fentanyl injected and the number of injections of dicolfenac sodium (75 mg each) requested by each of the group was then compared. Pain assessment was performed using a visual analog scale during resting periods (rVAS) and during swallowing (sVAS) for 9 days after the operation. The number of dicolfenac sodium injections and the total amount of fentanyl injected decreased significantly in the gabapentin group (P < 0.01). The sVAS of the gabapentin group was also significantly lower than that of the control group at 2 and 4 h after surgery, but there were no significant differences in the sVAS observed between the two groups for the remainder of the postoperative period. There were no significant differences in the rVAS observed between the two groups throughout the postoperative period. Thus, premedication with gabapentin decreased post-tonsillectomy pain. So the addition of gabapentin prior to tonsillectomy may have an adjunctive role in pain control.