We describe 11 premature infants with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). The syndrome is far more common than the single case report in the literature would indicate. All the infants had either asphyxiation at birth, intracranial hemorrhage, or meningitis. Of the nine children available for follow-up observation, seven demonstrated serious neurological sequelae. The diagnosis of SIADH in the premature neonate may be difficult to establish due to the complexity of precipitating factors.