Islet cell dysmaturation syndrome (ICDS) encompasses the causes of infantile hyperinsulinemic hypoglycemia histologically described as islet cell hyperplasia, pancreatic adenomatosis and nesidioblastosis. Eleven infants underwent 14 pancreatic resections for ICDS from 1965 to 1990 at the University of California at Los Angeles Medical Center for severe hypoglycemia unresponsive to medical therapy. Seizures were the presenting symptoms of hypoglycemia in eight infants. Six patients had nesidioblastosis, four had islet cell hyperplasia and one patient had an adenoma with histologically normal pancreatic islet cells. Four neonates underwent 80 per cent pancreatic resection; three with nesidioblastosis required reoperation (90 to 95 per cent resection). Four older infants underwent 80 per cent pancreatic resection but required diazoxide for less than six months postoperatively. Three infants underwent 90 to 95 per cent pancreatic resection. None have required reoperation or postoperative medications. All infants are normoglycemic without pancreatic exocrine insufficiency and none had postoperative complications. Five infants had preoperative neurologic impairment, with three having severe retardation; all showed some improvement postoperatively, but only one infant now has normal findings on neurologic examination. Early diagnosis and aggressive surgical resection should minimize neurologic complications of the ICDS.