Propylthiouracil is a drug used commonly to treat hyperthyroidism. Among its side effects, hepatotoxicity is one of the rarest but one of the most serious. This complication may be due to an immune mechanism. However, particular risk factors associated with the development of hepatotoxicity are not known, and its occurrence is unpredictable. I report a case of acute hepatitis developing during propylthiouracil therapy for Graves' disease and review the literature related to this problem.