OBJECTIVE: To determine the long-term outcome of neonatal dehydration. STUDY DESIGN: We identified 182 newborns who were rehospitalized with dehydration (weight loss > or =12% of birth weight and/or serum sodium > or =150 mEq/L) and 419 randomly selected controls from a cohort of 106,627 term and near-term infants with birth weight > or =2000 g born between 1995 and 1998 in northern California Kaiser Permanente hospitals. Outcomes data were obtained from electronic records, interviews, questionnaire responses, and neurodevelopmental evaluations performed in a masked fashion. RESULTS: Follow-up data to age at least 2 years were available for 173 of 182 children with a history of dehydration (95%) and 372 of 419 controls (89%) and included formal evaluation at a mean age (+/-standard deviation) of 5.1 +/- 0.12 years for 106 children (58%) and 168 children (40%), respectively. None of the cases developed shock, gangrene, or respiratory failure. Neither crude nor adjusted scores on cognitive tests differed significantly between groups. There was no significant difference between groups in the proportion of children with abnormal neurologic examinations or neurologic diagnoses. Frequencies of parental concerns and reported behavior problems also were not significantly different in the 2 groups. CONCLUSIONS: Neonatal dehydration in this managed care setting was not associated with adverse neurodevelopmental outcomes in infants born at or near term.