Autoimmune hemolytic anemia (AIHA) is subclassified according to the character of the autoantibodies, however, its clinical pictures are highly heterogenous even in a given subclass. In this article, we reviewed pathogenesis, clinical and laboratory characteristics of AIHA, exemplifying data of 26 patients with autoimmune hemolysis with warm-type autoantibodies (13 AIHA, 10 Evans' syndrome, 3 systemic lupus erythematosus), and recent advances in this field. White blood cell and platelet counts varied among patients at presentation. Six of 13 AIHA patients had low reticulocyte production index (RPI) indicative of inappropriate reticulocyte response with considerable erythroblasts in the bone marrow, suggesting that ineffective erythropoiesis contributes the pathogenesis of warm-type AIHA. Ten patients were judged to require red cell transfusion. Their RPI did not differ from that of patients who did not require transfusion, indicating that the degree of hemolysis is the major determinant of the severity of the disease. No significant side effects of transfusion were observed.