The most common cause of hyperinsulinaemic hypoglycaemia in adult is insulinoma. Although nesidioblastosis is a rare but well-recognized disorder of persistent hypoglycaemia in infants, it is extremely rare in adults.We present a case of a 59-year-old woman with small neuroendocrine tumour of the tail of the pancreas, diagnosed by CT scans and MRI, and hypoglycaemic syndrome. Laparoscopic distal pancreatectomy was performed, and pathologic examination showed a well-differentiated, non-functioning endocrine tumour of the pancreas and diffuse nesidioblastosis in the remnant gland. In the early postoperative period, recurrent hypoglycaemia occurred in spite of oral diazoxide therapy. Plasma proinsulin levels were extremely high. 18F-DOPA positron emission tomography showed a pathologic uptake of tracer in the head and the uncinate process of the pancreas. Subtotal pancreatectomy was suggested but the patient refused operation: she is taking diazoxide 100 mg three times daily. Coexistence of nesidioblastosis with a neuroendocrine tumour makes preoperative diagnosis and management of severe hypoglycaemia more difficult. Nesidioblastosis should be considered in differential diagnosis of hypoglycaemic syndrome, but histological examination is necessary for a definitive tissue diagnosis.