The osmotic demyelination syndrome (ODS) is a neurologic complication associated with rapid correction of hyponatremia. A case is described in which the patient was found to have hypokalemia as well as hyponatremia prior to the development of ODS. The literature was reviewed for cases of ODS in which patients had hyponatremia (serum sodium < or = 126 mmol/L) at presentation followed by correction of the hyponatremia. Of the 74 cases in which serum sodium and serum potassium values were reported at the time of presentation, 66 patients (89%) had hypokalemia. In 20 of these cases, serial measurements of sodium and potassium were reported, and in no instance was the potassium level normalized prior to the time of most rapid correction of the serum sodium. Hypokalemia may predispose patients to develop osmotic demyelination following correction of hyponatremia. The etiology of this complication is unclear. In neurologically stable patients with severe hyponatremia, it may be beneficial to correct hypokalemia prior to correction of the serum sodium. This maneuver may further reduce the incidence of ODS.