Hyponatremia has been reported with the use of psychotropic drugs. Olanzapine does not find much mention as a cause of hyponatremia in literature; however, it has been found to be the second most frequently reported atypical antipsychotic to cause it. We report a case of hyponatremia due to syndrome of inappropriate antidiuretic hormone secretion which occurred at a rapid onset following the administration of low-dose olanzapine during inpatient treatment of a patient with bipolar disorder. We would like to highlight our case for the need to be vigil about such fatal side complications apart from metabolic side effects of atypical antipsychotics.