Hyponatremia secondary to syndrome of inappropriate secretion of antidiuretic hormone (SIADH), which is characterized by the sustained release of antidiuretic hormone (ADH) from the posterior pituitary gland, is a less-known but life-threatening complication of treatment with antipsychotic medications. We report a patient who was using olanzapine due to the diagnosis of schizophrenia and presented with status epilepticus. The patient's medical history and biochemical blood and urine test results were suggestive of SIADH and revealed that hyponatremia was secondary to SIADH, induced by olanzapine use. The patient was treated succesfully with olanzapine discontinuation, fluid restriction, and hypertonic/normal saline infusion. The possible adverse effects of olanzapine on sodium-water balance should always be kept in mind while prescribing it, and we suggest that clinicians should closely monitor electrolytes, particularly sodium, in patients on atypical antipsychotic medications such as olanzapine.