An iontophoretic fentanyl HCl patient-activated transdermal system (fentanyl HCl PATS) is under development for the treatment of acute postoperative pain. The fentanyl HCl PATS is a needle-free, credit card-sized, preprogrammed system that is applied to the patient's upper outer arm or chest. The fentanyl HCl PATS was demonstrated to be superior to placebo in a previous trial; however, the randomization scheme used and the lack of control of entry pain level may have contributed to the lack of robust findings. We compared the fentanyl HCl PATS with placebo for acute postoperative pain management in a larger trial that addressed the limitations of the previous study. Adult patients admitted to the postanesthesia care unit after major surgery were titrated to comfort with opioids and randomized 1:1 to receive the fentanyl HCl PATS 40 microg or placebo for 24 hours. Supplemental IV fentanyl was available to patients upon request in both treatment groups for the first 3 hours after enrollment. The primary efficacy end-point was the percentage of patients who discontinued participation in the study because of inadequate analgesia. Pain intensity scores, patient global assessments (PGA), and investigator global assessments (IGA) were collected. Four-hundred-eighty-four patients (PATS, n = 244; placebo, n = 240) were enrolled. Fewer patients receiving the fentanyl HCl PATS discontinued because of inadequate analgesia compared with placebo (28.7% versus 60.0%; P < 0.0001). Mean last pain intensity scores were 3.5 and 5.4 for the fentanyl HCl PATS and placebo groups, respectively. Patients (73.4%, PGA) and investigators (72.1%, IGA) considered the fentanyl HCl PATS a good or excellent method of pain control. Treatment-related adverse events were similar between groups. This study demonstrated the superiority of the iontophoretic fentanyl HCl PATS over placebo for acute postoperative pain management.