Seven infants with hypernatremic dehydration developed subdural effusions or bleeding. One of these was a previously normal infant accidentally poisoned by excessive ingestion of salt. This infant and five of the others had significant neurologic damage, ranging from moderate to severe. It appears that the hypernatremic dehydration was responsible for the subdural lesions in these patients and responsible for permanent damage in at least three of them. Changes in chemical anatomy and lesions of the cerebral vessels are discussed with regard to producing lesions of the central nervous system in hypernatremic dehydration. At present no salutary therapeutic approach to the complication of subdural effusions occurring during hypernatremic dehydration has been found.