We performed serial magnetic resonance imaging (MRI) toward 4 male children with possible Pelizaeus-Merzbacher disease (PMD). They were clinically suspected as PMD on the basis of typical neurological, electrophysiological and MRI examinations. MRI revealed that myelinated fibers were localized in brainstem, cerebellum, internal capsule, optic radiation and proximal corona radiata in case 1, while myelinated fibers were almost absent in case 2-4. On repeated MRI investigation, we found no further extension of myelination in case 1 and the absence of myelination in case 2-4. This study demonstrated that myelination in the brain is arrested immediately after birth in case 1, while no myelination developed before birth in case 2-4. It was speculated that MRI in case 1 and case 2-4 might correspond to neuropathologic findings of classical and connatal form as reported in the literature.