Rapid correction of profound hyponatremia in a dog may have led to delayed neurological dysfunction five days later. The initial electrolyte abnormalities were due to Trichuris vulpis gastrointestinal parasitism. A presumptive diagnosis of myelinolysis was made based on the rapid correction of the hyponatremia and the clinical signs. Myelinolysis is a demyelinating brain disease caused by a rapid increase in plasma osmolality. Most naturally occurring cases of myelinolysis reported in the literature have been following rapid correction of hyponatremia due to Trichuris vulpis. The dog recovered, but still has some permanent neurological dysfunction. By following guidelines for proper correction of hyponatremia and prudent monitoring of plasma electrolytes, myelinolysis, an iatrogenic disease, can be prevented.