A 54-year-old woman was admitted due to high-grade fever, cervical lymphadenopathy and general malaise in May 2003. On examination, severe anemia was noted, direct Coombs and cold hemagglutinin tests were positive and the haptoglobin level was low in the peripheral blood. However, a bone marrow examination revealed marked erythroid hypoplasia. A diagnosis was made of co-existing combined type autoimmune hemolytic anemia (AIHA) and erythroid hypoplasia. A pathologic diagnosis of de novo CD5-positive diffuse large B-cell lymphoma (de novo CD5+ DLBCL) was made based on a cervical lymph node biopsy. The patient was treated with CHOP accompanied by rituximab (R-CHOP), resulting in complete remission after 3 courses of chemotherapy. The AIHA and erythroid hypoplasia subsided after 2 courses of R-CHOP. The sera obtained during erythroid hypoplasia significantly inhibited the growth of erythroid progenitor cells (erythroid colony-forming units, CFU-E) from her bone marrow collected after recovery. We report here a patient with de novo CD5+ DLBCL associated with both AIHA and erythroid hypoplasia, suggesting that the lymphoma triggered an abnormal immunity which generated some humoral inhibitors against erythropoiesis.