BACKGROUND: A randomized, double-blind, controlled study was conducted in patients undergoing elective knee arthroscopy to assess the analgesic effect of intraarticular bupivacaine alone and the combination of bupivacaine and clonidine. METHODS: Patients in bupivacaine group (n=15) received 0.125% bupivacaine 20 ml, patients in the bupivacaine and clonidine group (n=15) received a combination of 0.125% bupivacaine 20 ml and 150 microgram clonidine. These drugs were injected each other intraarticularly. We assessed postoperative pain by visual analogue scale (VAS) score at 1, 2, 3, 6, 12 and 24h after intraarticular injection. The need for supplemental analgesia was recorded. And the side effects of two groups were evaluated. RESULTS: VAS scores were significantly increased at 6hr after surgery than other times in bupivacaine group (p<0.05), but there was no significant difference of VAS score in bupivacaine and clonidine group. And in bupivacaine and clonidine group, VAS scores were significantly lower than that in bupivacaine group at 6 hr and 12 hr after surgery (p<0.05). Analgesic requirment was not used in bupivacaine and clonidine group, but 9 patients in bupivacaine group requires analgesics. Side effect in both groups, like hypotension and bradycardia, did not occur. CONCLUSIONS: Intraarticular 150 microgram clonidine with 0.125% bupivacaine 20 ml was significantly reduced postoperative pain following knee arthroscopy without side effect.