BACKGROUND: Patient-controlled analgesia (PCA) provides excellent pain relief in the management of postoperative pain, but is associated with unpleasant side effects such as nausea and vomiting. The transdermal scopolamine patch (TSP) has been shown to have effective antiemetic actions. We evaluated the effectiveness of TSP in patients receiving morphine and fentanyl via intravenous PCA. METHODS: Sixty patients were scheduled for an elective intra-abdominal gynecologic surgery under general anesthesia, and had elected to receive intravenous PCA postoperatively. Soon after their arrival in the operating room, the patients were randomised to receive either a placebo patch (group P) or TSP (group S) on the right postauricular area. Nausea, vomiting and sedation were scored at the postoperative care unit (PACU) and at 12, 24, 48, and 72 h postoperatively. Patients were treated with metoclopramide as deemed necessary by the primary care nurse. RESULTS: No differences were found between the groups in scores and incidence of nausea and vomiting at the PACU and at 12, 24, 48, and 72 h postoperatively. The patients who received metoclopramide were significantly fewer in group S than in group P (6.7% vs 43.3%, P < 0.05). The sedation score was significantly lower in group S than in group P (1.3 0.5 vs 1.8 0.9, P < 0.05) at 12h postoperatively. CONCLUSIONS: TSP did not reduce the incidence and score of nausea and vomiting in postoperative patients during intravenous PCA. However, patients who received TSP required less antiemetic medication. TSP appears to be effective for supplemental antiemetic medication.