A retrospective single-blind study assessing the value of magnetic resonance imaging (MRI) in 48 patients treated surgically for temporal lobe epilepsy was carried out. The imaging findings were correlated with the surgical findings in all cases. Abnormal MRI signals were detected in 34 of 48 (71%) epileptic patients and in 3 of 48 (6.2%) normal or disease control subjects. Twelve patients had structural foreign-tissue lesions, all detected by MRI. Of 14 patients with severe gliosis of the neocortex and/or mesial temporal structures, 11 had abnormal MRI scans. In patients with mild or moderate gliosis of mesial temporal structures, 6 of 12 had abnormal MRI scans. These results indicate that MRI is a sensitive technique for localizing foreign-tissue lesions, mesial temporal sclerosis, and gliosis in patients with intractable temporal lobe seizures.