A large family in whom 4 of 13 children were affected with hyperinsulinism of variable severity is described. The oldest affected child required subtotal pancreatectomy to control the hypoglycemia, but the three younger children were managed successfully with prolonged conservative therapy with maintenance oral doses of diazoxide. The three affected school-age children in the family have deficits in the areas of visuomotor integration and short-term memory. The three youngest children have normal intelligence compared with four unaffected siblings; only the oldest child, who has undergone pancreatectomy, has low-average intelligence (IQ80). We conclude that in infants with persistent but asymptomatic hyperinsulinemic hypoglycemia every effort should be made to treat conservatively with antihypoglycemic agents such as diazoxide for as long as possible to allow for spontaneous remission and thereby avoid pancreatectomy.