Background: Emergence agitation is a transient confusional state that usually occurs within 10 to 30 minutes of recovery from general anesthesia. It may lead to serious consequences and increasing hospital costs. This study evaluates the effect of gabapentin on emergence agitation in patients undergoing breast cancer surgery.Methods: This randomized, double blind controlled trial enrolled 100 female patients with American Society of Anesthesiologists' classifications I and II who were candidates for breast cancer surgery. Patients were randomly assigned into two groups (n=50) that received either oral gabapentin 600 mg or placebo. Induction and maintenance of anesthesia were similar in both groups. At the end of surgery, patient's agitation score, pain score, and presence of nausea or vomiting were reported. In the ward, the presence of headache or dizziness was checked during the first 8 h. Mann- Whitney test was used for comparison of agitation and pain scores between two groups. Chi-square test was used for comparing occurrence of nausea, vomiting and qualitative. The qualitative demographic variable and t-test compared quantitative demographic variables.Results: There was a significantly lower incidence of emergence agitation in the gabapentin group before (P<0.001) and after (P=0.029) extubation. There were significantly lower mean agitation scores before (P<001) and after (P=0.006) extubation and in the pain score (P=0.005) in the gabapentin group. The need for remifentanil infusion (P<0.05) during surgery was significantly lower in the gabapentin group compared with the placebo group. Occurrence of nausea and vomiting and gabapentin side effects that included headache or dizziness did not significantly differ between two groups (P=0.126, P=1, P=0.629 respectively).Conclusion: Gabapentin not only decreased postoperative pain but also effectively reduced emergence agitation without any significant side effects in patients undergoing breast cancer surgery.