BACKGROUND: Since postoperative cognitive impairement is common in elderly patients and normal cognitive function is important for proper use of patient controlled analgesia (PCA), we compared the efficacy, adverse effect and postoperative cognitive impairment among postoperative elderly patients given the PCA morphine, fentanyl and meperidine. METHODS: Forty-five elderly patients were randomly allocated to receive patient-controlled analgesia with either morphine, fentanyl or meperidine following upper abdominal surgery. Patients were evaluated for used doses, adverse effects, visual analogue scale, the satisfaction for analgesia during postoperative 2 days and the Mini Mental Status Examination (MMSE) and the Short Portable Mental Status Questionnaire (SPMSQ) at posoperative 1 day. RESULTS: Patients receiving the PCA fentanyl used more opioid based on a dose expressed as morphine equivalents using the putative potency ratios of 1:10:0.01 (morphine/meperidine/fentanyl). But adverse effects, visual analogue scale, and the satisfaction for analgesia were not statistically different between groups. The decrease in MMSE in the PCA-meperidine group was significantly greater than that seen in the PCA-fentanyl group and the PCA-morphine group. SPMSQ were not statistically different between groups. CONCLUSION: The present result suggest that PCA is effective method in posterative elderly without serious complications. But PCA meperidine may be avoided in the elderly because it can contribute to decrease postoperative cognitive function.