BACKGROUND: Intraarticular opioids and local anesthetics may provide effective analgesia following knee arthroscopic surgery. However, there are conflicting results about the analgesic effects of a combination of morphine, bupivacaine and clonidine injected intraarticularly following knee arthroscopic surgery. The goal of this study was to determine whether clonidine added to an intraarticular morphine- bupivacaine combination provide an analgesic benefit. METHODS: Thirty patients scheduled for knee arthroscopic surgery under epidural anesthesia were selected and divided to two groups randomly. The patients in Group 1 received a combination of morphine 3 mg 0.25% bupivacaine 30 ml and patients in Group 2 received a combination of clonidine 3microgram/kg and morphine 3 mg in 30 ml of 0.25% bupivacaine intraarticularly following knee arthroscopic surgery. Postoperative pain was assessed using the visual analogue scale (VAS) and changes of arterial blood pressure, heart rate, requirement of additional analgesics, adverse effects and sedation scale were observed at 1, 2, 4, 8 and 24 hours after intraarticular injection. RESULTS: The VAS observed at 4, 8 and 24 hours after intraarticular injection were significantly lower in group 2 than group 1. Blood pressure and heart rate were not significantly changed between group 1 and group 2. The incidence of side effects, injection of additional analgesics and sedation were similar between the groups. There were no significant differences in hemodynamic changes, analgesic requirements, sedation scale or the increase of side effects between group 1 and group 2. CONCLUSIONS: The results suggest that the combination of intraarticular morphine 3 mg in 30 ml 0.25% bupivacaine plus clonidine provides significantly better analgesia than morphine 3 mg in 30 ml 0.25% bupivacaine alone following knee arthroscopy.