A 62-year-old female was admitted to our hospital for examination of icterus and thrombocytopenia. She had a history of diabetes mellitus (under treatment), and liver cirrhosis was evident on abdominal CT. Because she was clinically obese and had no past history of alcohol consumption, the initial diagnosis was NASH. However, subsequent MRI findings and normal serum transaminase levels were not consistent with this diagnosis. We then performed additional examinations, including liver biopsy, measurements of serum Cu and ceruloplasmin concentrations, and measurement of urinary Cu secretion, which resulted in a diagnosis of Wilson's disease. It is necessary to include Wilson's disease in the differential diagnosis of NASH in cases of unidentified liver disease even among elderly patients.