A 36-year-old womanwho had had Graves' disease for 6 years was admitted with severe thrombocytopenia. Evans' syndrome was diagnosed. The patient's family history showed multiple cases ofGraves' disease but no cases ofEvans' syndrome. Both conditions in this patient improved with corticosteroid and thiamazole therapy. Several autoimmuneantibodies were found, but a commonautoimmunemechanism was not clearly shown. Although the combination of Graves' disease and Evans' syndrome had not occurred previously in her family, genetic factors may play an important role in the pathogenesis of both conditions. (Internal Medicine 35: 987-990, 1996)