The purpose of this study was to compare the efficacy of postoperative pain control by intravenous patient-controlled analgesia (IV) and by continuous intralesional infusion of a local anesthetic (IL) with or without an interscalene block (ISB) after arthroscopic shoulder surgery. We allocated 84 patients to 4 groups according to analgesic method: IV, ISB-IV, IL, and ISB-IL. Postoperative pain, side effects, and supplementary analgesics were recorded at 1 hour and then every 8 hours for 48 hours. The interscalene block (groups ISB-IV and ISB-IL) was found to be effective at relieving pain and at reducing supplementary analgesic amounts at 1 and 8 hours postoperatively (P < .05). Patients in group ISB-IL had less pain at 16 and 48 hours postoperatively than those in the other groups (P < .05). Continuous intralesional infusion (groups IL and ISB-IL) was superior in reducing analgesic-related side effects (P < .05). This study suggests that a combination of an interscalene block and continuous intralesional infusion of a local anesthetic is an effective and safe method of postoperative pain control after arthroscopic shoulder surgery.