Hyponatremia and rapid correction of hyponatremia have often been proposed as pathogenetic mechanisms in the development of central pontine myelinolysis. We report the case of a 36-year-old man who died with acute hemorrhagic pancreatitis with the autopsy findings of central pontine and extrapontine myelinolysis. The patient had developed moderate serum hyperosmolality during the first 3 days of his illness, and it persisted until his death 20 days later. Hyponatremia or rapid correction of hyponatremia never occurred. These observations suggest that osmotic stress and oligodendrocyte topography rather than rapid correction of hyponatremia may be the key to the development of central pontine myelinolysis (osmotic myelinolysis).