BACKGROUND: An effective control of postoperative pain may contribute to success of day-case surgery. After knee arthroscopy, local anesthetics was injected into the knee joint to reduce postoperative pain, but results were variable and the duration of action may be short. The recent reports have suggested that intraarticular morphine would provide more effective and longer acting analgesia than expected from the same dose given systemically. METHODS: A randomized, controlled study was conducted in patients undergoing elective knee arthroscopy under general anesthesia to assess the analgesic effect of intraarticular bupivacaine and morphine, either alone or in combination. Patients in group I(n=20) received 20 ml of normal saline as a control; patients in group II(n=20) received 20 ml of 0.25% bupivacaine; patients in group III(n=20) received 5 mg of morphine in 20ml of normal saline; patients in IV(n=20) received a combination of 5 mg of morphine and 50 mg of bupivacaine in 20 ml of normal saline. All the drugs were injected intraarticularly. Postoperative pain was assessed using the VAS at 1, 2, 4, 8, 12, and 24h after the intraarticular injection. Whenever patients want supplemental analgesia, 90 mg of diclofenac(dicknol ) was injected intramuscularly and then the need for supplemental analgesia was recorded. RESULTS: Patients in groups III and IV had significantly lower pain scores than those in groups I and II. There was no significant difference in the pain scores or analgesics requirements between groups III and IV. CONCLUSIONS: We conclude that intraarticular morphine(5 mg) significantly reduces postoperative pain following knee arthroscopy and there is no significant advantage of combining bupivacaine with morphine.