Although cases of hyponatremia during pregnancy have been de- scribed, it has rarely been possible to show demyelination lesions in central pons, bulbus as well as thalamus, by imaging techniques. We report a case that developed extensive myelinolysis due to the "rapid" correction of hyponatremia as a result of hyperemesis gravidarum. Magnetic resonance imaging showed bilaterally symmetric hyper- intense areas in the thalamus and cerebral crus and symmetric hy- perintense area in the central pons, with sparing of the rim. In the second day of hospitalization, probably as a result of expansion of myelinolysis, she was intubated and received mechanical ventilator due to bradypnea and a GCS scale of E1M4V2. She was extubated in 11th day of hospitalization and physical therapy was started. She was discharged in 30th day of hospitalization with a GCS of 15. But she was tetraparetic (2/5). In the 3rd month of follow up, her quadri- paresis improved to paraparesis in lower extremities (3/5). Her follow up examinations in the first year did not change although physical therapies go on. She delivered a normal child.