In adults, endogenous hyperinsulinemic hypoglycaemia is almost invariably due to insulinoma. The authors describe a 29 year old patient with repeated postprandial symptomatic hypoglycaemias and negative prolonged fast test. Distal pancreatectomy was performed, directed by positive arteriographic testing. Histological examination revealed pancreatic nesidioblastosis and no tumoral lesion. Distinct pathogenetic, clinical, diagnostic and therapeutic aspects of this rare disease in the adult are reviewed.