A foal developed signs of neurological dysfunction two days after rapid correction of severe electrolyte derangements, including hyponatremia, caused by chronic diarrhea. History, laboratory findings, and onset of neurological signs following correction of hyponatremia led to a presumptive diagnosis of myelinolysis. Myelinolysis is a noninflammatory, demyelinating brain disease caused by sudden, upward osmotic shifts in the central nervous system plasma, often a result of rapid correction of chronic hyponatremia. The pathogenesis is largely unknown. Iatrogenic damage due to myelinolysis can be avoided by adherence to therapeutic guidelines for correction of chronic hyponatremia. The diagnosis of myelinolysis ultimately could not be confirmed by either MRI or histopathology.