We recently demonstrated that the prognosis for de novo CD5-positive (CD5+) diffuse large-B-cell lymphoma (DLBCL) is markedly worse than that for CD5-negative (CD5−) DLBCL. Our findings also suggested that on the basis of its clinical features CD5+ DLBCL may constitute a unique disease category. However, the genetic basis for these two categories has not been established. Therefore, we performed comparative genomic hybridization analysis (CGH) of 26 cases of CD5+ DLBCL and 44 cases of CD5− DLBCL. Several identical changes in CD5+ and CD5− DLBCLs were found, such as gains of 3q, 9p, 12q, 13q, and 18q and losses of 1p, 6q, 17p, and 19p. However, distinct differences between the two categories were also detected. These included gains of 11q21-q24 (P = 0.032) and 16p (P = 0.005) in CD5+ DLBCL, and loss of 16p (P = 0.028) in CD5− DLBCL. A comparison with results reported for mantle cell lymphoma, chronic lymphocytic leukemia, and Richter's syndrome demonstrated that the CGH pattern of CD5+ DLBCL was markedly different. This indicates that CD5+ DLBCL constitutes a disease category distinct from that of CD5− DLBCL and other CD5+ malignancies. © 2003 Wiley-Liss, Inc.