A 27-year-old male developed massive generalized lymphadenopathy with chronic myelomonocytic leukemia (CMML) presenting as extramedullary blast crisis mimicking a lymphocytic lymphoma. On presentation, a consistent chromosomal abnormality involving chromosomes 8 and 13, i.e. 46, XY, t(8;13) (q11;p11), was present in lymph node tissue, bone marrow and unstimulated peripheral blood. The appearance of trisomy 21 in addition to the presence of the original cytogenetic abnormality is simply regarded as clonal evolution, i.e. 47, XY, t(8;13)(q11;p11),+21. The importance of the cytogenetics lies in finding the same abnormality in bone marrow and lymph node, adding evidence that the immunologically similar cells in the two sites have arisen from a common progenitor cell. To our knowledge, this novel chromosomal abnormality has not been reported in association with a unique case.