AbstractMany nonrandom chromosome abnormalities have been associated with non‐Hodgkin's lymphomas (NHL). Some of these are nonspecific changes seen in many different histologic subtypes. We describe a series of abnormalities of chromosome bands 10q23–25 seen in 159 consecutive NHL patients with abnormal cytogenetic findings. The proportion of karyotypes with abnormalities of 10q varied from 3% among the immunoblastic lymphomas to 67% in the diffuse large cleaved cell lymphomas. Seventeen (10.7%) had abnormalities of 10q23–25. All but one of these were B‐cell tumors. The abnormalities consisted of six deletions and 11 translocations. Sixteen of the 17 patients had the 10q abnormality when cells were first karyotyped. The remaining patient acquired the 10q abnormality in the third of a series of biopsies. In the follicular histologic subtypes [follicular small cleaved cell (FSC), follicular mixed small cleaved and large cell (FM), and follicular large cell noncleaved (FL‐NC)], abnormalities of 10q were found in nine patients, all in association with abnormalities of 14q32. Seven of these were associated with the t(14;18)(q32;q21). Overall, 10q23–25 abnormalities were observed in 11.9% (8/67) of low‐grade [small lymphocytic (SL), FSC, and FM] lymphoma cases. DNA was available from five patients with abnormalities of 10q and was probed for rearrangements with the HOX11 (TCL3) oncogene probe. As expected, we did not find such rearrangements in these five patients with B‐cell tumors. Abnormalities of 10q23–25 have been reported previously in NHL but not at this frequency.