Three autopsy cases of pontine and extrapontine myelinolysis are reported; one, a malignant lymphoma in a man of 66 years, the other an alcoholic liver cirrhosis in a man of 54 years, and an esophageal cancer in a woman of 68 years who presented only with extrapontine myelinolysis, but lacked central pontine myelinolysis (CPM). The extrapontine lesions in these three cases revealed a characteristic and common localization; they occurred mostly in the bundles of myelinated fibers in the gray matter, such as in the pons, basal ganglia, and thalamus; and in the white matter surrounded by massive gray matter, such as the deeper layers of the cortex and subjacent white matter of the crowns and sides of the cerebral gyri, the white matter of the cerebellar folia and internal, external, and extreme capsules. Therefore, the third patient was classified as a subtype of pontine and extrapontine myelinolysis, which may be called the "extrapontine form" because of absence of CPM. Moreover, bilateral demyelination of the mamillary body was found in all cases, and laminar cortical astrocytosis and necrosis similar to Morel's cortical laminar sclerosis in two of them. From the clinical and pathologic findings, the significance of the changed osmolarity of the blood as a cause and the importance of some specificity of the tissue architecture in the pathogenesis are discussed.