Oxcarbazepine and carbamazepine cause hyponatremia by unknown mechanisms. We de-scribe a patient with complete central diabetes insipidus and seizures who developed wors-ening hyponatremia when her dose of oxcarbazepine was increased. The patient maintained a normal serum sodium level and has had appropriately concentrated urine for 5 years on just oxcarbazepine, despite undetectable antidiuretic hormone (ADH) levels. This suggests that oxcarbazepine (or one of its metabolites) may stimulate collecting tubule V2 receptor-G protein complex independent of ADH, resulting in increased renal tubular water reabsorp-tion. Oxcarbazepine may be useful as an alternative therapy for patients with central diabetes insipidus. [ABSTRACT FROM AUTHOR]