Spontaneous hyperinsulinism resulting from a tumour of the islets of Langerhans is not a common condition, and the diagnosis is easily overlooked. Failure in diagnosis usually results in the early death of the patient, while diagnosis followed by operative removal of the tumour cures the majority of patients.Nicholls (1902) first described an adenoma of the islet cells of the pancreas, but this was an incidental finding at necropsy and no clinical details of the case were recorded. Following the discovery of insulin, Harris (1924) suggested that symptoms might be caused by excess secretion of the hormone, and the first demonstration of an insulin-secreting tumour was by Wilder et al. (1927); they explored the pancreas of a doctor, aged 40, who had suffered from attacks of spontaneous hypoglycaemia for eighteen months, and found a carcinoma in the tail of the pancreas with metastases in the liver. The cells of the carcinoma bore a striking resemblance to islet cells, and insulin was extracted from one of the liver metastases.The first successful operative removal of an insulinsecreting tumour was by Roscoe Graham in 1929(Howland et al., 1929, who found a small tumour in the body of the pancreas of a woman of 52 who had a seven-years history of attacks of spontaneous hypoglycaemia. The tumour was composed of islet cells, and as it lacked a capsule it was thought possibly to be a carcinoma, but no metastases were found. This lack of a capsule has been a feature of a number of islet-cell tumours subsequently studied, and is not now regarded as an indication of malignancy. Another successful operation was performed at about the same time, for Harvey Cushing (1930), in his Lister Lectures on neurohypophysial mechanisms, mentioned that a small islet-cell adenoma which had caused recurrent attacks of hypoglycaemia had recently been removed in his clinic. Since then the condition has attracted much attention in the United States, no fewer than 38 cases being reported from the Mayo Clinic in twenty years (Lopez-Kruger and Dockerty, 1947), while reviews have been published on both medical (Crain and Thorn, 1949) and surgical aspects of the problem (Howard et al., 1950).In Great Britain the number of reported cases is comparatively small. Apart from Nicholls's early pathological observation, the first report is that of Barnard (1932), who found an islet-cell adenoma at the post-mortem examination of a patient in whom the diagnosis had been suspected clinically but who had declined further investigation or operation; postmortem reports have also been published by Cairns and Tanner (1933)