We report a patient who developed cholestatic jaundice shortly after initiation of treatment with metformin hydrochloride. Ultrasound of the liver and abdominal CT were normal. An ERCP showed normal biliary anatomy. A percutaneous liver biopsy was obtained showing marked cholestasis, with portal edema, ductular proliferation, and acute inflammation. Metformin hydrochloride was discontinued, and the patient's jaundice resolved slowly over a period of several months. Given the onset of his jaundice 2 wk after the initiation of metformin, we believe that this case represents an example of metformin-associated hepatotoxicity, the first such case reported.