Data on chromosomal abnormalities in T-cell lymphomas are very rare as compared with those reported in B-cell lymphomas. We performed a cytogenetic study in 71 untreated patients with peripheral T-cell lymphoma, classified according to the criteria of the REAL classification. Fifty-seven patients (80.3%) had abnormal clones, whereas 9 karyotypes (12.7%) showed only normal metaphases; 5 karyotypes (7%) could not be analyzed. Recurrent numerical chromosomal abnormalities comprised +3 (21%), +5 (15.7%), +7 (15.5%), +21 (14%), -13 (14%), +8 (12.2%), +19 (12.2%), -10 (10.5%), and -Y (9% of male patients). Chromosomes involved in structural rearrangements were chromosome 6 (31.5%), mainly due to 6q deletions (19.2%), 1q (22.8%), 7q (22.8%), 9p (19.4%), 9q (19.2%), 4q (19.2%), 3q (19.2%), 2p (17.5%), 1p (17.5%), and 14q (17%). Trisomies 3 and 5 mainly correlated with angioimmunoblastic T-cell lymphoma. Isochromosome 7q, associated with trisomy 8, was present in two cases of hepatosplenic gamma/delta T-cell lymphoma. Rearrangements involving the location of T-cell receptor genes were rarely observed (chromosome band 7q35 was rearranged only in three cases, 14q11 in two cases, and 7p15 in none). No correlation could be found between the cytogenetic findings and histologic subgroup or clinical outcome in these patients. Further studies are needed to understand the significance of these abnormalities in peripheral T-cell lymphoma, and to reach a better evaluation of histologic correlations, as many differences persist between the two major classification systems, KIEL and REAL.