To determine the type and rate of secondary chromosomal aberrations and role in pathogenesis of mantle cell lymphoma (MCL).Standard cytogenetic examination (SCE) and fluorescent in situ hybridization (FISH) with tests for 11q22/ATM, 13q14, 17p13/p53, 9p21/p16 and chromosome 12 centromere were made in 28 patients.Secondary chromosomal aberrations were detected in 22 patients. Chromosomal abnormalities occurring in more than 2 cases include deletions 6q15-q23 (53% cases); 11q22/ATM (50%); 9p21 (36%, in half the cases deletion 9p21 was biallele); 13q14 (32%); trisomy 3/3q, monosomy 20 and deletions/translocations 1q and 1p (27% and 20%) and deletion 17p13/p53 (18%). Trisomies 12/12q, 6 and 18/18q, monosomies 2 and 16, deletions/translocations 2p and 16p were found in 2 cases each. The FISH technique identified 9 chromosomal anomalies missed at SCE. Deletions 6q15-q23 were seen in patients with privalent lesions of lymph nodes. Deletions 11q, 13q14, 9p21 and 17p13 occur more frequently in transformation and the blastoid variant. Monosomy 20 was found only in patients with large cell transformations. This was the only cytogenetic defect characteristic for transformed cases, in contrast to denovoblastoid ones. Thus, deletions 6q, 11q23, 13q14 and 9p21 are typical for MCL. Deletions 9p21 and 17p13 are more characteristic for large cell variants of the tumor. Deletion 17p13 occurs at the terminal stage of the disease in rapidly growing tumor mass and resistance to chemotherapy. FISH technique is effective in detection of submicroscopic rearrangements especially small deletions. No significant differences were found between transformed and de novo blastoid cases. This shows that the blastoid variant is not a specific biological form, it is rather a less typical manifestation of the disease due to some preclinical cytogenetic disorders.Progression and transformation of MCL are related to mutation of proapoptotic genes and genes proteins of which are inhibitors of active complexes of D1 cycline. Specification of these mechanisms requires further investigations in patients with different clinicomorphological forms of the disease at various stages of the disease.