A 31-year-old woman with Graves' disease with a 12-month-history of propylthiouracil intake and autoantibodies in the sera was admitted to our hospital. The differential diagnosis between autoimmune hepatitis and propylthiouracil-induced hepatitis was intractable. Steroid therapy was started and she showed a complete response to the treatment. Liver biopsy demonstrated acute hepatitis and plasma cell infiltration. A second liver biopsy, which was performed 10 months after starting steroid therapy, showed some inflammatory cells in the portal tracts. These findings suggest that she had been suffering from autoimmune hepatitis.