Fifty of approximately 250 patients evaluated for intractable partial seizures were shown to have a space-occupying lesion detected with radiographs and/or neuroimaging. Twenty-eight males and 22 females had a mean age at seizure onset of 13 years and a mean duration of seizures of 11 years. All patients had closed-circuit television with EEG monitoring and complete neurologic and neuropsychological assessment. Findings were correlated with lesion location and surgical data. Twenty-seven lesions (54%) were located in the temporal lobe. Thirty-five lesions (70%) were neoplastic. All patients with temporal lobe lesions had complex partial seizures, as did 74% of patients with extratemporal lesions. A good correlation between clinical seizure characteristics and lesion localization was found with the temporal, occipital, and frontal lesions but not with the parietal lesions. Sixty-six percent of patients had focal interictal EEG findings. Lateralization corresponded to the side of the lesion in 64% and was localized to the region of the lesion in 30%. Lateralized ictal EEGs occurred in 58% of patients, corresponding with the side of the lesion in all but one patient. Abnormal findings on neuropsychological testing were congruent with lesion lateralization in 56% of patients and were localized to the region in 26%. Thirty-nine of 47 patients who underwent a subtotal lobectomy to include the lesion are seizure-free after greater than or equal to 1 year of follow-up, and five others are markedly improved.