A 72-year-old man presented with a tentative diagnosis of acute leukemia. His white cell count was 7.59 × 103/µL, including 15.0% leukemic cells with immature morphology. Lactate dehydrogenase value was 4,243 IU/L. The bone marrow biopsy showed ‘packed’ marrow infiltration of leukemic cells. The cells were CD5−, CD10+, CD19+, CD20+, and surface immunoglobulin γλ+ by flow cytometry, and BCL2+, BCL6−, and MUM1− by immunohistochemistry. 18Fluorodeoxyglucose-positron emission tomography combined with computed tomography showed heterogeneous tracer uptake throughout the bone marrow space. G-banding of leukemia cells revealed a hyperdiploid karyotype with two copies of t(14;18)(q32;q21), and fluorescence in situ hybridization of interphase nuclei confirmed the double t(14;18)(q32;q21). There was no 8q24/MYC rearrangement. Long-distance polymerase chain reaction generated a 2.6 kilobase-pair product, encompassing the major breakpoint cluster of BCL2, N-like segments, and the J5 segment of the immunoglobulin heavy chain gene. Although, the patient initially responded to chemotherapy, he relapsed shortly and died of disease progression. This case represents a rare presentation of follicular lymphoma, in which transformation to aggressive disease occurred de novo without a preceding indolent phase. It is possible that the double t(14;18)(q32;q21) may have generated a higher amount of BCL2 protein, thereby accounting, in part, for the progressive/refractory behavior of this case.