Five patients with lymphocytic malignancies were found to have structural aberrations of chromosome 14, all involving band q11. The malignant cells of all five cases were analyzed by immunofluorescence to establish immunologic phenotypes. Three patients had T lymphoblastic lymphoma/leukemia with mediastinal masses (cases 1, 2, and 3); one patient had peripheral T cell lymphoma (case 4); and one patient had acute lymphocytic leukemia, common acute lymphoblastic leukemia antigen positive (case 5). Although aberrations of chromosome 14 frequently are associated with lymphocytic malignancies, these abnormalities most often result in extra material on the long arm, 14q+. However, none of the five patients reported here had a 14q+. Cases 1 and 2 had t(9;14)(q34;q11) and t(11;14)(p11 or 13;q11), respectively. Case 3 showed del(14)(q11), and cases 4 and 5 showed inv(14)(q11q32). Structural aberrations resulting in 14q- and inv(14) appear to occur infrequently. The five cases in this report, in conjunction with those found in the literature, indicate a strong association between breaks at 14q11 and T lymphocytic malignancies.