Over a 14-year period 34 patients were referred for surgical treatment of insulinoma. The diagnosis was confirmed by demonstrating hypoglycaemia with inappropriate hyperinsulinaemia during prolonged fasting. Selective visceral angiography localized 30 solitary benign insulinomas and two carcinomas. In two patients with islet cell hyperplasia, angiography demonstrated a single lesion only. Ultrasonography had a sensitivity of 15 per cent and computed tomography a sensitivity of 24 per cent in the localization of tumours. All patients but one were treated by operation. Eighteen tumours were enucleated and 13 (including both patients with islet cell hyperplasia) were treated by distal pancreatectomy. Two patients underwent negative primary exploration; both had single adenomas removed at re-exploration. There were no operative deaths but nine patients (predominantly those undergoing pancreatic resection) had complications. Thirty-one patients were symptom-free following operation at a mean follow-up of 16 months.