Machiafava-Bignami disease (MBD) occurs in the alcoholic patients. It is characterized clinically by interhemispheric disconnection syndrome, resulting from demyelination and necrosis of the corpus callosum. We performed a neuropsychological study of an alcoholic patient, diagnosed as MBD by X-ray computed tomography (CT) and magnetic resonance imaging (MRI). 123I IMP-SPECT of the patient revealed the reduction of the blood flow in both cerebral hemispheres without laterality though both the X-ray CT and MRI showed no abnormality in the cerebral hemispheres. In neuropsychological studies, we observed not only interhemispheric disconnection syndrome such as an unilateral left agraphia and left apraxia but also left hemispatial neglect demonstrated in right-hand performance and motor impersistence. Because there were no abnormal lesions in the right hemisphere, these symptoms might be attributable to the lesions of corpus callosum.