We reported a case of late infantile neuronal ceroid-lipofuscinosis. The patient was an 8-year-old boy presenting with marked psychomotor deterioration, progressive visual failure due to retinal degeneration and optic atrophy, startle reaction to auditory stimuli, frequent myoclonus and generalized convulsions. The routine laboratory examinations were all normal. EEG was markedly abnormal because of poorly organized background activity and frequent paroxysmal spike-and-wave complexes. CT scan showed evidence of severe atrophy of the cerebrum, cerebellum and brainstem. Electron microscopic examination of the biopsied rectum revealed fingerprint profiles in the neurons and pericytes beneath the muscularis mucosa. Cultured skin fibroblasts also contained electron dense inclusions, some of which showed fingerprint profiles. Urinary glycopeptides were normal. Lyscsomal enzyme activities in leukocytes and cultured fibroblasts were normal. Neurophysiological studies revealed giant cortical potentials evoked by the auditory as well as somatosensory stimulation. Simultaneous recording of the somatosensory evoked EEG and EMG potentials disclosed that the myoclonus in this patient was stimulus-sensitive and compatible with the cortical reflex myoclonus. With regard to hypothetical pathogenesis of this disease, we studied lipoperoxide in the blood before and after anti-oxidant therapy. We also measured vitamin A and carotene, since these substrates are related to retinoic acid. Although vitamin A and carotene were normal, lipoperoxide was slightly elevated. However, it was not influenced by the treatment with anti-oxidant. Significance of elevated lipoperoxide to the pathogenesis of this diseases has not solved.