In 231 diffuse large B-cell lymphomas, the expression of cyclin D1 and CD5 was evaluated. All cases were CD5-. Ten (4.3%) were positive for cyclin D1 and were subjected to fluorescence in situ hybridization at the CCND1 locus. One case showed the t(11;14). In another case, the telomeric probe signal for cyclin D1 was lost in most tumor cells, and in a small proportion of the cells, there were fluorescence signals indicative of the t(11;14). Two other cases displayed additional cyclin D1 signals in the absence of the t(11;14). All cases but 1 were positive for bcl-6 or MUM1, disfavoring the possibility of misdiagnosed blastoid variants of CD5- mantle cell lymphomas. Thus, contrary to the current view, there seems to exist a certain number of cyclin D1+ and CD5- diffuse large B-cell lymphomas, some of which have structural aberrations at the CCND1 locus, including the t(11;14).