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Purpose: This prospective, randomized, single-blind study evaluated the efficacy and pharmacokinetic profile of a transdermal delivery system for fentanyl to provide relief of acute postoperative pain in patients undergoing intra-abdominal gynecologic surgery for cancer. Methods: Forty female patients were randomized to either transdermal fentanyl 50 µg/hour (n = 20) or transdermal placebo (n = 20). Transdermal systems were placed 1 hour preoperatively and removed 25 hours later. Pain control was supplemented with a nonopioid drug, bupivacaine 0.125–0.25%, administered through an epidural catheter via patient-controlled epidural analgesia. Serum fentanyl concentrations, bupivacaine consumption, pain scores [visual analog scale (VAS)], sedation rating score, adverse events, and physiological parameters were recorded for 48 hours postoperatively. Results: The minimum effective concentration of fentanyl in serum (0.63 ng/mL) was achieved at 11.3 ± 4.9 hours after application, and serum concentrations remained above this level until 13 hours after removal. The TTS-F group had lower VAS pain scores and a significant 66% reduction in utilization of bupivacaine compared with placebo. Pain scores were significantly correlated with serum fentanyl concentration (P = 0.025). All physiological parameters fluctuated within normal range and no differences were observed between treatments. Adverse events were similar between the groups with only the incidence of local erythema significantly higher in the TTS-F group (30% vs. 5%, P