Control of postoperative pain is an important element in preventing the modification of the excitability of the dorsal horn neurons. We studied the efficacy of bupivacaine 0.5% wound infiltration for postoperative pain management following thyroid surgery. Forty consecutive ASA I-II patients, scheduled for thyroidectomy, were assigned randomly to two groups. Group I (n = 20) consisted of patients receiving bupivacaine 0.5% (10 ml) wound infiltration at the end of surgery and group II (n = 20 included patients without infiltration. The patients did not know whether the wound had been anaesthetized or not. All patients received balanced inhalational anaesthesia, including fentanyl (a total dose of up to 4 micrograms.kg-1). Postoperative pain medication included morphine IV or IM, as needed. Twenty-four hours after surgery the worst pain was recorded using a visual analogue scoring system, from 0 to 10. Twenty-four hour postoperative morphine requirement was recorded. Groups did not differ in demographic data. Pain scores significantly different in the two groups. In group I, the mean pain score was 3.7 +/- 1.6 compared with 6.9 +/- 1.7 in group II (P < 0.05). Only six patients (30%) in group I received opioids and only one of these (5%) had a pain score above 5. In comparison, 18 patients (90%) in group II received morphine during the first postoperative day. The local injection of bupivacaine corresponds to a block of the superficial branches of the cervical plexus. This study demonstrated a simple, efficient and safe way to reduce pain perception following a thyroidectomy.