The best-known adverse hematologic reaction of methimazole is agranulocytosis. Aplastic anemia is extremely rare. The prognosis within the entity of aplastic anemias is surprisingly good, despite the severe and prolonged course of the disease. The present article reports the case of a 74-yr-old female patient who exhibited aplastic anemia with severe clinical symptoms 8 weeks after the initiation of methimazole administration. The hemorrhagic symptoms were aggravated by a coumarin overdose. Supportive hemotherapy and antibiotic treatment were supplemented with recombinant human granulocyte colony-stimulating factor and high-dosage corticosteroids. The granulocyte count normalized on day 5 of treatment, the platelet count exceeded the critical value on day 11, and on day 25 the patient was discharged in remission.