BACKGROUND: The purpose of this study was to compare the relative analgesic efficacies of the postoperative intra-bursal infusion of bupivacaine, bupivacaine/morphine, and bupivacaine/fentanyl after shoulder arthroscopy. METHODS: At the end of subacromial arthroscopy, a continuous intra-bursal infusion catheter was inserted. A bolus dose was injected via the catheter just after the operation and a maintenance dose was infused for 4 days (1 ml/h). The bupivacaine group (Group B, n = 25), received 10 ml of 0.5% bupivacaine and 96 ml of 0.25% bupivacaine. The bupivacaine/morphine group (Group BM, n = 25) received 2 mg of morphine in 10 ml of 0.5% bupivacaine and 8 microgram of morphine in 96 ml of 0.25% bupivacaine. And the bupivacaine/fentanyl group (Group BF, n = 25) received 100 microgram of fentanyl in 10 ml of 0.5% bupivacaine and 400 microgram of fentanyl in 96 ml of 0.25% bupivacaine. VAS at rest and exercise were evaluated preoperatively and postoperatively for 3 days. The frequency of IM rescue analgesic were recorded. RESULTS: We did not find any significant differences in VAS, or in need for rescue analgesic between the three groups. Resting pain score was significantly reduced at the 2 nd- and 3 rd postoperative day versus the preoperative value in Group B and BM, and at the 3 rd postoperative day in Group BF (P < 0.05). Pain score at exercise was reduced at the 3 rd postoperative day versus the preoperative value in all groups (P < 0.05). CONCLUSIONS: The combination of morphine or fentanyl with bupivacaine did not provide better postoperative analgesia than bupivacaine after shoulder arthroscopy.