A case of primary interhemispheric subdural abscess was reported, which was not accompanied by abscess formation in other places such as subdural spaces of the convexity or in the brain. A 13-year-old school boy was admitted with 8 days' history of fever, headache and progressive weakness of the left lower extremity. Prior to admission he developed 2 spells of jacksonian seizure initiating from the left leg. Right carotid angiography was performed on admission and separation of the pericallosal and callosomarginal arteries with small avascular area was shown indicating possible abscess formation in the interhemispheric fissure. There was no evidence of purulent infection in the laboratory findings including the CSF and EEG showed diffuse slow wave discharge, more in the right frontocentral leads. He was placed on the vigorous treatment with antibiotics and steroids, and one month later the left lower weakness as well as the EEG abnormality showed some improvement. However, the separation of the anterior cerebral arterial branches became more prominent and formed a lens shaped avascular area, although the pericallosal artery was in the midline. A diagnosis of interhemispheric subdural abscess was made and was confirmed by surgery. Patient showed progressive recovery of the left lower paralysis, and the abscess was totally collapsed in the repeated angiographic follow-up study. Angiographic characteristics of the interhemispheric subdural abscess were described and particular emphasis was placed on the peculiar neurological symptoms referring to the previous reports in the literature.