Summary: The case of a 33-year-old patient suffering from severe hypoglycaemia due to an insulinoma during the first trimester of pregnancy is reported. The diagnosis was established on clinical grounds and by the demonstration of hypoglycaemia, inappropriate hyperinsulinism and an increase in the percentage of circulating proinsulin. Dietary therapy maintained blood glucose at a satisfactory level from the 9th to the 17th gestational week. Localization of the tumour was achieved at that time by limited CT scanning with a narrow field. A 2 cm tumour was removed from the head of the pancreas and the blood sugar levels and insulin secretion returned to normal. Pregnancy proceeded normally and a healthy male infant weighing 3,880g was delivered at term. Ten months after delivery both mother and child were well.