We report the occurrence of a cytogenetically abnormal clone 46,XX,t(1;6)(p35;q23),t(1;9;19)(q23;p24;q13) in the spleen of a 23-year-old woman with a three-year history of angiocentric immunoproliferative lesion (AIL) (lymphomatoid granulomatosis). The skin, lungs, spleen, liver and, focally, bone marrow were involved by atypical lymphohistiocytic infiltrates. Immunophenotypic study of the spleen showed that 46% of the cells displayed a helper/inducer T-cell phenotype. However, analysis of DNA isolated from the spleen failed to show clonal T-cell receptor beta-chain gene, T-cell receptor gamma-chain gene, or immunoglobulin heavy chain gene and light chain gene rearrangements. The finding of a cytogenetically abnormal clone supports the concept that angiocentric immunoproliferative lesion is a neoplastic process.