Objective To study efficacy and safety of hypertonic saline administration in the management of hyponatremic seizures. Design Retrospective, observational, cross-sectional study with factorial design. Setting In-patient population in a university hospital. Patients All children admitted with serum sodium concentrations <125 mmol/L. Sixty-nine episodes of severe hyponatremia in 60 children were reviewed. Forty-one of these children presented with seizures. Interventions Twenty-five of 41 seizure patients received an iv bolus of 4 to 6 mL/kg body weight of 3% saline. Twenty-eight patients were treated with a benzodiazepine and/or phenobarbital with or without the subsequent administration of hypertonic saline. Measurements and Main Results Thirteen treatment failures and ten instances of apnea occurred among the 28 patients treated with benzodiazepine/phenobarbital. Administration of hypertonic saline resulted in resolution of seizures and apnea in all cases. Those patients receiving 3% saline had a higher serum sodium increase rate from 0 to 4 hrs than the remaining patients (3.1 ± 1.3 vs. 1.7 ± 1.2 mmol/L-hr, p < .01). None developed subsequent neurologic deterioration or clinical manifestations of osmotic demyelination syndrome. Conclusion Treatment of hyponatremic seizures with routine anticonvulsants may be ineffective and is associated with a considerable incidence of apnea. A rapid increase in the serum sodium concentration by 3 to 5 mmol/L with the use of hypertonic saline is safe and efficacious in managing acute symptomatic hyponatremia. (Crit Care Med 1991;19:758)