This case describes a young girl with Graves' disease, who presented with fulminant hepatic failure 9 months into propylthiouracil (PTU) therapy. Her clinical presentation was consistent with 'probable autoimmune hepatitis,' as defined by the International Autoimmune Hepatitis Group scoring system. Despite discontinuation of PTU and high-dose steroid therapy, she required liver transplantation. Subsequent pathology could not definitively rule out autoimmune hepatitis. PTU is an important cause of drug-related liver failure in children, and clinicians should be mindful that it is frequently used in patients who already have an underlying risk of autoimmune liver disease.