One hundred patients with intractable temporal lobe epilepsy and 22 control subjects were scanned on a 1.5-T Siemens SP63 Magnetom scanner. A combination of hippocampal T2 mapping, hippocampal volume measurement corrected for intracranial volume, and inspection of hippocampal morphology on a hippocampal volume distribution graph compared with a control graph revealed previously undetected forms of bilateral hippocampal sclerosis and four false-positive diagnoses of hippocampal sclerosis made on visual inspection of the scans. A physiological asymmetry in the position of the hippocampi in 41% of control subjects and focal hippocampal atrophies in patients made measurement of the whole length of the hippocampus mandatory. The extent of hippocampal damage in patients with hippocampal sclerosis correlated with the number of secondary generalized seizures during a patient's lifetime. In contrast to patients with unilateral hippocampal sclerosis, patients with severe bilateral hippocampal sclerosis had no history of febrile convulsions. Twenty-six patients with intractable temporal lobe epilepsy had normal hippocampal magnetic resonance imaging measures and as a group were significantly older at the onset of habitual epilepsy than were patients with hippocampal sclerosis. In conclusion, a combination of quantitative magnetic resonance imaging techniques revealed a spectrum of hippocampal sclerosis and optimally defined boundaries of hippocampal normality. The spectrum of hippocampal sclerosis is related to the etiology, the number of secondary generalized seizures, and the age at onset of habitual epilepsy.