We compared conventional cytogenetic findings in mantle cell lymphomas (MCLs) having an absolute peripheral lymphocytosis of more than 10,000/microL (>10 x 10(9)/L) at diagnosis ("leukemic"; n = 30) with those in cases having no or minimal lymphocytosis ("nodal"; n = 19). Only cases positive for t(11;14) were included for study. Forty-six cases (94%) had abnormalities in addition to t(11;14). The most frequent abnormalities involved chromosome 13 (26 cases [53%]), followed by chromosomes 1, 3, 7, 8, 9, 10, 12, 15, 17, and 21 (11-18 cases [22%-37%]). There was no difference in the number of aberrations between the 2 groups. Abnormalities of chromosomes 17, 21, and 22 were more frequent, and breakpoints involving 8q24, 9p22-24, and 16q24 were found exclusively in leukemic MCL. Chromosome 17 aberrations involved were structural (breakpoints involving 17p13, 17p11.2, 17q) in leukemic MCL but were only numeric in nodal MCL. Thus, leukemic MCL differs from nodal MCL in their cytogenetic profiles, which may contribute to the clinical presentation.