Depression is the most frequent comorbid psychiatric disorder in epilepsy. Its lifetime prevalence has been estimated at between 6% and 30% in population-based studies and up to 50% among patients followed in tertiary centers. The risk of suicide has been estimated to be 10 times higher than that in the general population. Although no one questions that epilepsy is a risk for depression, recent studies have also revealed that a history of depression is associated with a 4- to 6-fold greater risk of developing epilepsy. These data suggest either a possible "bi-directional" relationship between these two disorders or the presence of common pathogenic mechanisms that facilitate the occurrence of one in the presence of the other. The clinical presentation of depressive disorders in epilepsy can be identical to that of nonepileptic patients and can include major depression, bipolar and dysthymic disorders, and minor depression. In a significant percentage of cases, however, the clinical features of depression in epilepsy fail to meet any of the DSM-IV Axis I categories. Depression in epilepsy may be iatrogenically induced with various antiepileptic drugs used to treat the seizure disorder or after surgical treatment of intractable epilepsy. Despite its relatively high prevalence, depression remains unrecognized and untreated, and unfortunately its treatment is based on empirical and uncontrolled data.