Rapid-onset hyponatremia as well as rhabdomyolysis are rare, but potential, complications of olanzapine treatment. Hyponatremia, secondary to atypical antipsychotic use, has been reported in many case reports and is thought to be associated with a syndrome of inappropriate anti-diuretic hormone secretion (SIADH). We report a case of sudden-onset hyponatremia associated to a sever rhabdomyolysis resulting in a coma necessitating intensive care unit admission. His evolution was favorable after correction of all his metabolic disorders and Olanzapine suspension.