Severe hyponatremia with hypoosmolality carries a high morbidity and mortality and constitutes a life-threatening emergency. We report seen cases of severe hyponatremia (serum sodium concentration 99.7 +/- 3.0 meg/liter) (mean +/- SEM) with hypoosmolality (212 +/- i mOsm/kg water) that presented with severe neurologic complications. Serum sodium concentration was corrected in 13.3 +/- 2.2 hours to mildly hyponatremic levels (serum sodium concentration 128.3 +/- 1.6 meq/liter). The rate of correction of serum sodium concentration was 2.4 +/- 0.5 meq!liter/hr. This was achieved by the intravenous administration of 3 percent hypertonic saline solution (687 +/- 43 meq sodium chloride) and furosemide or by hemodialysis where indicated. No complications occurred from treatment and all of our patients recovered without neurologic sequelae. Early diagnosis and rapid correction of serum sodium concentration appear to reduce the significant morbidity and mortality of severe hyponatremia.