The study of chromosomal changes related to tumor progression in NHL is complicated by the various histologic classification systems and the lack of large serial studies comparing abnormalities at different disease stages. The T-cell lymphomas frequently involve rearrangements of the T-cell receptors and tumor progression is marked by a change from single cell aberrations and polyclonality in low grade disease to monoclonal formation, complex clones, polyploidy, and abnormalities of 1p, 6q, 7, and 13 in high grade T-NHL. In B-cell NHL, specific translocations and oncogene rearrangements are associated with specific NHL subtypes de novo; many of these translocations involve immunoglobulin genes, such as t(14;18) in follicular lymphoma, t(11; 14) in MCL, t(3;14) in DLLC, and t(8;14) in Burkitt's lymphoma. Tumor progression is associated with secondary abnormalities which are generally not confined to a particular NHL subtype. Some abnormalities, such as those involving chromosomes 1, 6, and 17, >4-6 clonal markers/cell, and rearrangements of c-MYC and TP53, have prognostic significance while others, such as trisomies 7, 12, 18, and X., are associated with tumor progression but their influence on overall survival is uncertain.