We describe a 65-year-old woman with follicular lymphoma (FL), grade 1, stage IV, which occurred concurrently with B lymphoblastic leukemia/lymphoma. Through the evaluation of FL, the cells that were morphologically suspected of having undergone transformation were found in the bone marrow, and flow cytometric and cytogenetic analyses detected the transformed population that suggested concomitant t(8;22) with typical t(14;18) FL cells. Repeated analyses of the lymph nodes demonstrated the typical morphological, phenotypic, and cytogenetic features of FL. The patient received several multiagent chemotherapy regimens, but the disease gradually became resistant, and the patient died of leukemic progression. In B-cell malignancies, cases involving both BCL2 and MYC translocations simultaneously, so-called "double-hit leukemia/lymphoma (DHL)", have occasionally been reported. Patients with this type of translocation have a very poor clinical outcome, and no standard therapy has been established. In our case, FL was supposed to have transformed into B lymphoblastic leukemia via Burkitt's lymphoma-like phase. Our case is unique in that the transformed DHL cells, derived from clonally related FL cells, showed ongoing transformation from Burkitt-like feature to B lymphoblastic leukemia exclusively in the bone marrow, which suggests that the bone marrow may provide a preferable milieu for malignant transformation. Similar cases should be accumulated and analyzed carefully.