Two dogs developed delayed neurological deterioration after rapid correction of severe hyponatremia. Sequential magnetic resonance imaging showed the development of lesions in the thalamus. One dog was necropsied, and the lesions were characterized by myelinolysis with sparing of axons and neurons. The second dog gradually recovered with no detectable neurological deficits. The syndrome seems analogous to central pontine myelinolysis in human beings. Guidelines for correction of hyponatremia to prevent development of myelinolysis are given.