Severe autoimmune hemolytic anemia is described as the presenting manifestation of malignant thymoma. The hemoglobin level was 5.7 g/dl, the direct IgG antiglobulin test (direct Coombs' test) was strongly positive and the indirect Coombs' test was weakly positive. Prompt remission of the hemolytic process was achieved by thymectomy combined with corticosteroid therapy; the hemoglobin level rose to 12.2 g/dl and both the direct and indirect Coombs' tests became negative. To our knowledge, this is the first case to be described in which autoimmune hemolytic anemia was the presenting manifestation of malignant thymoma. Autoimmune hemolytic anemia may be considered as a manifestation associated with malignant thymoma.