BACKGROUND: A number of studies indicate that aerosol spray lidocaine and non-steroidal anti- inflammatory drugs (NSAIDs) provide good postoperative analgesia for both minor and major surgeries. The aim of this study was to compare the analgesic and side effects of topical lidocaine spray with that of ketorolac after a tonsillectomy. METHODS: In a double blind, randomized manner, sixty ASA class 1 or 2 patients were selected for a tonsillectomy under general anesthesia. All patients received propofol 2 mg/kg and vecuronium 0.1 mg/kg followed by a propofol infusion of 6 - 10 mg/kg/h in O2/N2O 40%/60%. At the end of surgery, the patients were divided into three groups and given no drug (group 1, n = 20), given 2 mg/kg 10% lidocaine sprayed to posttonsillectomy sites (group 2, n = 20) or given intravenous ketorolac 0.5 mg/kg (group 3, n = 20). Postoperative pain was assessed using the visual analogue scale (VAS) score at 30 minutes, 1, 2 and 4 hours after full recovery and the side effects of the three groups were evaluated. RESULTS: The VAS of group 2 was significantly lower than that of other groups at 30 min after recovery (P = 0.00). At 1 h, the VAS of group 2 and 3 were significantly lower than that of group 1 (P = 0.00), and the VAS of group 2 was significantly lower than that of group 3 (P = 0.02). At 2 and 4 hrs, the VAS of groups 2 and 3 were significantly lower than that of group 1 (P = 0.00), but the difference was not significant between groups 2 and 3. Side effects such as hoarseness, oral paresthesia, swallowing difficulty and oral bleeding were observed. However, the intensity of side effects was mild. CONCLUSIONS: 10% lidocaine spray and intravenous ketorolac injection produce a significant analgesic effect without specific complications after a tonsillectomy. In control of immediate postoperative pain, 10% lidocaine spray has a better effect than that of intravenous ketorolac injection.