The osmotic demyelination syndrome includes pontine and extrapontine myelinolysis, the first being its classic form of presentation. Usually related to rapid corrections of hyponatremia (serum sodium less than 135mEq/L), it has been described in multiple conditions that can alter plasma osmolality. The symptoms are varied and include spastic tetra paresis, pseudobulbar paralysis, coma, seizures or the characteristic “locked in” syndrome, as well as behavioral disorders such as lack of impulse control, aggressiveness, depressive syndromes, catatonia, mutism, and emotional lability. Years ago, it was a very difficult entity to diagnose, but with the introduction of magnetic resonance imaging, many oligosymptomatic or asymptomatic cases have been detected, although there is no known treatment, spontaneous recovery can occur.