Introduction: The 'rapid' correction of hyponatremia, itself a dangerous to the patient involved. There is an association between the 'rapid' correction of plasma sodium and the osmotic demyelination syndrome, characterized by the loss of myelin in the pontine neurons, and in extra- pontine sites such as the internal capsule, basal ganglia, cerebellum and cerebrum. Although cases of hyponatremia during pregnancy have been described, it has rarely been possible to demonstrate the condition, by imaging techniques or autopsy, showing demyelination lesions of the cerebrum. We report the case of a pregnant patient who developed this complication nd had an interesting response to levodopa. Clinical case. A 27 year old woman had a history of progressive generalized muscle weakness for the previous six days. She had recently been discharged after receiving treatment for hyperemesis gravidarum. Imaging studies showed pontine and extrapontine myelinolysis. She was treated with levodopa which improved her extrapyramidal symptoms. Conclusions. Hyponatremia is the most commonly observed electrolyte disorder in the hospital population. The classical symptoms of myelinolysis are spastic quadriparesia and pseudobulbar paralysis, which reflect damage to corticospinal and corticobulbar paths. Serious symptomatic hyponatremia is a medical emergency which should be managed by specially trained personnel, since the treatment is as dangerous as the condition itself. More investigations are necessary to identify the precise risk factors and the mechanism by which an increase in sodium causes damage to myelin.