Purpose: Despite adequate epidural analgesia, up to 97% of patients undergoing thoracotomy experience ipsilateral shoulder pain. In this setting, this study evaluated the safety and the efficacy of pre-emptive gabapentin. Methods:A double-blind, placebo-controlled study was undertaken in 51 patients randomized into two groups. Two hours before surgery, 23 patients received gabapentin 1200 mg po (Group G), and 28 patients received placebo (Group P). Shoulder pain and postoperative pain, at the surgical site, were monitored every four hours for 24 hr, using a numerical rating scale. Subcutaneous hydromorphone was administered for rescue analgesia against shoulder pain. Results:Forty-four patients complained of shoulder pain (prevalence of 86%). Demographic and surgical data were similar between the two groups. There were no significant differences in the total cumulative doses of hydromorphone administered at eight, 16, and 24 hr, nor were there differences in individual numerical rating scale scores for shoulder pain. The groups were similar with respect to the degree of pain at the surgical site. The frequency of side effects between groups at corresponding time intervals was also similar, with the exception of sedation. At four hours, the incidence of sedation scores > 1 was greater in Group G (21/23 patients), compared to Group P (18/28 patients; P = 0.025). In contrast, by 24 hr, 5/18 patients in Group P had sedation scores > 1, compared to 0/28 patients in Group G (P = 0.05). Conclusion:Pre-emptively administered gabapentin, 1200 mg, does not reduce the incidence, or the severity, of post-thoracotomy shoulder pain in patients receiving thoracic epidural analgesia.