We report here a case of multiple sclerosis (MS) showing pure alexia. The patient was a 28 year-old, right-handed male student of medicine. He had been healthy prior to college, but when he tried to read the newspaper one morning in January of 1983, he suddenly became aware that he could not. He could speak fluently and had no disturbances of auditory comprehension. No signs of abnormality were noted in his writing ability. Thereafter, the patient occasionally experienced difficulty in reading, together with right homonymous hemianopsia. These symptoms, however, usually vanished following sleep. In April, 1984, the patient experienced headache and ataxia when walking, followed by repeated remission and exacerbation of the symptoms. Corticosteroid therapy produced complete disappearance of the headache and ataxia. In September of 1985, he was hospitalized at our department due to the clouding of consciousness accompanied by convulsions. Neurologically, no abnormalities of the ocular fundus were noted and Babinski's sign was negative, but left hemiplegia was observed. Neuropsychologically, his intelligence was normal and he had no difficulty in writing, but paralexia was noted. There were no disorders of spontaneous speech or auditory comprehension. Examination by CT scan and magnetic resonance imaging revealed a number of lesions in the white substance of the cerebrum, including the left occipital lobe. The abnormal signs seen radiographically vanished when cortical hormones were administered. It has been thought that the symptoms of multiple sclerosis are due mainly to disorders of the white substance, and that MS seldom produces symptoms of aphasia, due to the fact that the lesions in this disease are generally small.(ABSTRACT TRUNCATED AT 250 WORDS)