We studied the electroencephalograms (EEGs) of 154 patients with well-defined diencephalic, mesencephalic, or posterior fossa lesions. Electrographic and clinical parameters were statistically evaluated. The results indicated considerable overlap of EEG abnormalities from different subcortical sites. Focal or lateralized abnormalities were relatively specific, suggesting a diencephalic lesion, whereas bilateral paroxysmal slow-wave disturbances were unspecific and not of precise diagnostic significance. There was no specific feature in this series to clearly distinguish the EEG pattern in deep midline lesions from that seen with diffuse cortical and subcortical encephalopathies.