A large newborn infant with hemihypertrophy, omphalocele, hepatomegaly, left upper quadrant abdominal mass, and zoster-like skin rash had severe hypoglycemia at 4 hours of age. Serum immunoreactive insulin levels were markedly elevated. Hypoglycemia was not controlled by vigorous medical therapy but blood glucose levels returned toward normal following subtotal excision of the markedly hyperplastic pancreas at 24 days of age. At 4½ months of age, a right upper quadrant abdominal mass was noted and urinary adrenal steroid levels were elevated. The right adrenal gland was found to be markedly hyperplastic and it was removed; the left adrenal gland was slightly hyperplastic. Between the ages of 5 and 8 months the umbilical stump enlarged progressively forming a large pedunculated tumor which was removed. This patient presents an unusually severe example of Beckwith's syndrome with both prenatal and postnatal organ overgrowth, severe hypoglycemia and hyperinsulinism.