To determine the analgesic efficacy of dexmedetomidine in the early postoperative period. Randomized, double-blind, double placebo-controlled clinical trial. University medical center. 30 ASA physical status I, II, and III patients with cruciate ligament lesion and joint fibrosis who were scheduled for knee arthroscopy. Patients were prospectively randomized to receive dexmedetomidine one mcg/kg(-1) intravenously (IV), for 10 minutes followed by dexmedetomidine 0.3 mcg/kg(-1) for 50 minutes or propacetamol two g, IV, for 10 minutes. Pain scores, time to onset analgesia, and morphine consumption were measured. Open-label rescue morphine 5 mg IV was available as needed during the postdosing evaluation period of 8 hours. Hemodynamic data, sedation scores, and renal and hepatic function were assessed for control of adverse events. Pain scores with dexmedetomidine and propacetamol were similar. There were no differences in the number of patients who required supplemental rescue analgesia (7/15 vs 4/15; P = 0.44), but total morphine requirements were higher with dexmedetomidine (45 mg) versus propacetamol (20 mg) in the 8-hour follow-up (P < 0.05). The most frequent adverse events with dexmedetomidine were bradycardia and hypertension. Dexmedetomidine provides a modest analgesic effect after knee arthroscopy, but the side effects of this drug, such as hypertension and bradycardia, may restrict the use of large bolus doses.