During a three-month period, 15 patients under two years of age presented with serum sodium concentrations less than 127 mEq/L. Seven (47%) of these patients presented with seizures. Hyponatremia accounted for a majority (58%) of the afebrile seizures in children under two years during this period. Of the eight patients without seizures, four later proved to have cystic fibrosis. Most of the patients with seizures appear to represent the syndrome of infant water intoxication. Hyponatremia may account for more seizures in early life than has been appreciated. Physicians and parents should avoid dietary practices which promote water intoxication. The etiology, diagnosis, and management of water intoxication and hyponatremic seizures are discussed.