Patient-controlled analgesia (PCA) techniques are widely used for postoperative pain control, but the efficacy and safety of these modalities have been poorly evaluated in elderly Koreans. Therefore, we compared the effect of intravenous and epidural PCA on the postoperative pain and adverse events in elderly patients undergoing major abdominal surgery. Patients (> 65 years) who received intravenous PCA (IV PCA) or epidural PCA (PCEA) after major abdominal surgery under general anesthesia between March 2011 and March 2012 were included in the study. In the IV PCA group, patients received IV PCA using fentanyl (14-18 μg/kg) plus 8 mg of ondansetron or 0.3 mg of ramosetron, which was programmed to deliver 2 ml/h as a background infusion, and 0.5 ml per demand with a 15 min lockout. In the PCEA group, patients received PCEA using fentanyl (2-5 μg/ml) plus ropivacaine (0.10-0.20 %), which was programmed to deliver 5 ml/h as a background infusion and 2 ml per demand, with a 15 min lockout. Epidural catheters were inserted before surgery at a vertebral level corresponding to the dermatomal level of the surgical incision. For patients presenting with difficult thoracic epidural catheteriza tion requirements, epidural catheters were inserted near the site of surgical incision. At the end of surgery, IV PCA or PCEA was initiated. Two PCA nurse practitioners monitored patients in the postanesthesia care unit (PACU) and at 1-6, 6-12, 12-18, 18-24 and 24-48 hr intervals after surgery, inquiring about the occur rence of adverse events, the need for rescue IV analgesics (15-30 mg of ketolorac, 25-50 mg of tramadol or 25 mg of meperidine), and pain intensity scores. A total of 1024 patients were included in the study; 754 patients in the IV PCA group and 270 patients in the PCEA group. Patient characteristics, anesthesia and operative data were similar between the two groups except that female gender and ASA physical status ≥ III were more common in the IV PCA group. In the PCEA group, 72% of patients underwent laparotomy through an upper-mid abdominal incision. Patients who under went laparoscopic or robot-assisted surgery mostly were mainly treated with IV PCA (95%). While pain intensity was similar between the two groups in the PACU, it was significantly higher in the PCEA group from 1 to 48 h after surgery. The need for rescue analgesics was less in the IV PCA group compared to the PCEA group during 6 to 48 h following surgery. In subgroup analysis according to surgical site, pain intensity was similar throughout the study period between the two routes of administration among patients who underwent upper-mid laparotomy. However, in patients who underwent mid-lower laparotomy and laparoscopic or robot-assisted surgery, pain intensity was higher in the PCEA group compared to the IV PCA group during the first 1 to 48 h period and in the PACU to 48 h period, respectively (Fig. 1). There were no significant differences in adverse events including incidence of post-operative nausea and vomiting, headache and dizziness, urinary retention, or sedation between the two groups. Epidural analgesia has been reported to be superior to intravenous analgesia with respect to postoperative pain relief, bowel recovery, and patient satisfaction [1,2]; epidural analgesia has also been reported to be similar to intravenous analgesia in