Carbamazepine and oxcarbazepine are antiepileptic drugs which can induce hyponatremia, being this disorder more frequent with the latter.In this report we present a clinical case regarding an oxcarbazepine induced hyponatremia, and we hypothesized that oxcarbazepine could induce hyponatremia as a consequence of its influence on distal nephron where it could promote free water retention, urinary sodium loss, or both of them.Besides, we proposed that a greater tubular sesitivity to oxcarbazepine than to carbamazepine could explain the different hyponatremia inducing capability between these two drugs