A 44-year-old man was admitted because of persistent fever and pancytopenia. Because his bone marrow was hypoplastic and the karyotype of his marrow cells was normal, he was given a diagnosis of aplastic anemia, and treated with glucocorticoids and granulocyte colony-stimulating factor. Splenomegaly was later found and a splenectomy performed: pathological findings on resected tissue specimens disclosed non-Hodgkin's lymphoma, B-cell diffuse large. The patient was transferred to our hospital, where a bone marrow biopsy revealed lymphoma cells infiltrating his hypoplastic marrow. Complex chromosomal abnormalities were detected in marrow cells, but no lymphadenopathy was observed. A diagnosis of primary splenic lymphoma with infiltration of lymphoma cells into bone marrow was made, and chemotherapy was accordingly started. After multiple cycles of chemotherapy, the patient's marrow recovered to a normal state and his karyotype abnormalities disappeared. Six months later, pancytopenia reappeared and lymphoma cells were again detected in the patient's bone marrow. We reasoned that the hypoplastic state of his bone marrow was associated with the lymphoma, and that cytokines, including interferon-gamma, may have been responsible for this association.