The magnetic resonance imaging (MRI) appearance of the various histologic substrates of epilepsy and the clinical role of MRI in symptomatic epilepsy are reviewed. MRI is used clinically to identify potential surgical candidates among patients with epilepsy, assist in surgical planning, and help to determine the prognosis of patients with epileptic seizures. MRI can clearly characterize the morphologic substrates that underlie the electroclinical abnormalities noted in patients with epilepsy. The histologic substrates of symptomatic epilepsy can be divided into five major categories: tumors, disorders of neuronal migration and cortical organization, vascular malformations, mesial temporal sclerosis, and neocortical sclerosis attributable to brain injury (trauma, infection, inflammation, or infarction). Because of its ability to disclose subtle alterations in cortical architecture or changes in signal intensity, MRI is the most sensitive and specific imaging technique for the noninvasive identification of each of these substrates. Introduction of MRI into clinical practice during the past 10 years has substantially changed the management of patients with epilepsy.