Arthroscopic surgery of the knee is a common out patient procedure. Anesthesia for this kind of surgery should provide sufficient surgical conditions, good postoperative analgesia and early discharge from hospital and minimum side effects. The aim of this study was to evaluate the effects of intraarticular morphine and ketamine on postoperative analgesia and find out the side effects of them in the patients undergoing arthroscopy under spinal anesthesia. ASA I-II, 90 patients scheduled for arthroscopic surgery were included in this study. All patients operated under spinal anaesthesia. Spinal anesthesia was performed at L4-5 interspace with 10 mg 0.5% hyperbaric bupivacain. Patients were randomly allocated to receive intraarticular 0.1 mg kg1 morphine diluted with saline into 30 ml (group M, n=30) or intraarticular 0.5mg kg-1 ketamine diluted with saline into 30 ml (group K. n=30) or intraarticular 30 ml saline (group SF, n=30) at the and of the surgery. Visual analogue score at 4, 8, 12, 24 hr after surgery, ,duration of motor block, duration of first mobilization, the first pain feeling time, the VAS score during first mobilization, the number of patient requering rescue analgesic and adverse effects were recorded. VAS scores at 4, 8, 12, 24 hours and during first mobilization were lower in group M and K than in group SF. First analgesic rescue times were longer in group M (139.5±25.0) and group K'nin (145.5± 40.0) than group SF (124.2±16.2). The number of patients requiring analgesic in 24 hours was higher in group SF than group M and K. No side effect was seen in group M and SF but hallucination was observed in one patient in group K. Conclusion: Intraarticular morphine and ketamine provided better postoperative analgesia than saline group in outpatients requiring arthroscopic knee surgery under spinal anesthesia. However unwanted side effects might seen in ketamine group. That's why we belive that intraarticular morphine administration for postoperative analgesia is suitable in patient undergoing arthroscopic knee surgery.