OBJECTIVE A probable case of aripiprazole-induced syndrome of inappropriate antidiuretic hormone (SIADH) is reported. CONCLUSIONS A 65-year-old Caucasian man arrived in the emergency department (ED) with dizziness, headache, abdominal pain, nausea, and vomiting. There had been no recent additions or changes to the patient's medication regimen except for an increase in the daily dose of aripiprazole (from 10 to 20 mg) about two months prior. On admission, the patient's serum sodium concentration was 108 meq/L, prompting discontinuation of aripiprazole use and fluid restrictions. Over the next 72 hours, the serum sodium level increased to a near-normal concentration (127 meq/L), and the man was discharged back to a nursing facility. Three days later, the patient was readmitted to the ED with recurrent symptoms and a serum sodium concentration of 118 meq/L, a serum osmolality of 254 mOsm/kg, a urine osmolality of 575 mOsm/kg, and a urine sodium concentration of 101 meq/L. It was learned that aripiprazole use had been inappropriately resumed at the nursing facility. Aripiprazole was again discontinued, and fluid restrictions were imposed, with subsequent abatement of hyponatremia over four days. Application of the adverse drug reaction probability scale of Naranjo et al. in this case yielded a score of 7, indicating probable aripiprazole-associated SIADH. CONCLUSIONS A 65-year-old man developed severe hyponatremia after an aripiprazole dosage increase. Hyponatremia resolved promptly with the discontinuation of aripiprazole. After discharge from the hospital, the patient inadvertently received aripiprazole again and was subsequently readmitted with another episode of severe hyponatremia.