Effective pain control is important after an outpatient arthroscopic knee surgery to permit early discharge and improve outcome. The aim of this study was to compare intraarticular morphine and bupivacaine with placebo for postoperative pain control and outpatient status after a knee arthroscopic surgery under a low dose of spinal anaesthesia. After obtaining the ethic committee's approval and written informed consents from 60 adult outpatients undergoing knee arthroscopy, patients were enroled in this prospective, randomized, double-blinded, placebo-controlled clinical study. All patients received spinal anaesthesia with 1.4 ml of hyperbaric bupivacaine 0.5%. Patients were randomly divided into three groups as morphine (group M, n = 20), bupivacaine (group B, n = 20), and placebo (group C, n = 20). After the surgical procedure, patients received one of the following solutions intraarticularly in a double-blinded randomized manner: 5 mg morphine in 20 ml saline, 20 ml 0.25% bupivacaine, or 20 ml saline. Postoperative pain was assessed using a 10-cm visual analogue scale (VAS). Patient characteristics, hemodynamic values, sensory and motor blocks, VAS values, rescue analgesics, discharge time, and patient satisfaction were recorded. There were no significant differences in patient characteristics, surgery and tourniquet time, hemodynamic values, and sensory and motor blocks. The VAS values at 30, 60, and 90 min were similar among the three groups. The VAS values at rest and during move were higher in group C than in groups M and B at 120, 150, 180 min, and 24 h (P < 0.001). There was no difference in VAS values between the groups M and B. Rescue analgesics used and discharge time were significantly different in the placebo group when compared to groups M and B (P < 0.001). Side effects were similar among the groups. Patient satisfaction scores were high in the groups M and B. Administration of 5 mg morphine and 20 ml of 0.25% bupivacaine intraarticularly provides better pain relief and shorter discharge time without increasing the side effects than placebo for an outpatient arthroscopic knee surgery performed under a low dose of spinal anaesthesia.