We report the clinical, histological, immunophenotypic, and cytogenetic findings in ten patients with T-cell lymphoproliferative disorders demonstrating reactive "angioimmunoblastic lymphadenopathy with dysproteinemia (AILD)-type" features. Fifteen available specimens were diagnosed as atypical hyperplasias (four) or malignant lymphomas (11). The latter were classified as AILD-type (five), T-zone (four), lymphoepithelioid (one), and low-grade, unclassified lymphoma (one). Despite the histologic differences, all these lesions shared minor nuclear atypicalities and reactive AILD-type features such as prominent vascularity, plasma cells, eosinophils, macrophages, and residual germinal centers. All lesions were immunophenotyped as predominantly T cell. The chromosome pattern was characterized by the frequent presence of karyotypically unrelated abnormal clones and/or cells with nonclonal chromosome abnormalities, a large population of normal mitotic cells, and a high incidence of trisomies 3 and 5. Sequential cytogenetic and histologic studies in five patients revealed that atypical hyperplasia and lymphoma with AILD-type features shared the same cytogenetic characteristics, ie, an unstable coexistence of normal mitotic cells and small-clonal and/or nonclonal abnormal cells, and that histologic transformation from low-grade lymphoma to immunoblastic lymphoma was accompanied by a selective proliferation of abnormal clonal cells. The AILD-type histology and the characteristic karyotypic pattern may be the expression of a specific pathogenesis and may warrant the separation of these neoplasias from other peripheral T-cell lymphomas.