We have reviewed our experience with gangliogliomas treated in the post-computed tomography (CT) era at the Children's Hospital of Philadelphia. Of 234 newly histologically verified neoplasms seen at our institution since 1975, 10 (4.3%) were gangliogliomas of the cerebral hemispheres. The presenting complaint was seizures in 9 of 10 patients. and in 8 the seizures were poorly controlled despite increasing doses of anticonvulsant medication. At the time of diagnosis, only 2 patients had a focal neurological deficit and none had signs or symptoms of increased intracranial pressure. Learning disability and behavioral disturbances were common in this group of children. The CT appearance of these lesions was characteristic: most appeared as a cerebrospinal fluid density area that was located peripherally and often indented the skull. There was little contrast enhancement, and a few were diagnosed initially as arachnoid or porencephalic cysts. Despite the CT appearance, all but 2 of the lesions were found to be solid at operation. In one patient, the lesion appeared as an enhancing lesion of the thalamus, and this patient died. Operation resulted in symptomatic improvement. Eight of 9 children are alive, with a follow-up of 1 to 80 months (median, 19.5 months), and are free of progressive disease. Five are seizure-free while receiving anticonvulsant therapy and an additional 3 have improved seizure control as a result of operation. Two of the 3 children with intellectual difficulties preoperatively have shown improvement on testing after operation, probably the result of improved seizure control. One patient developed a disseminating malignancy and died. It is concluded that worsening seizures in the pediatric age group should warrant CT examination and that ganglioglioma should be included in the differential diagnosis of low density areas on CT.