An unusual hematologic neoplasia has been described recently in which the predominant clinical features include T-cell lymphoma, myeloid hyperplasia, and eosinophilia. The multilineage involvement in this disorder suggests transformation of a primitive stem cell. Abnormal karyotypes have been described in three such cases, including one case with t(8;13)(p11.2;q12) and a second case with t(8;13)(p23;q14). We report translocation of chromosomes 8 and 13 in lymph node karyotypes from two patients with this syndrome. Fluorescence in situ hybridization confirmed an identical translocation, t(8;13)(p11;q11-12), in lymphoma cells from each patient. The translocation breakpoints are of particular interest because the FLT3 receptor tyrosine kinase gene has been mapped 13q12. FLT3 is expressed highly in hematopoietic progenitor cells and in myeloid and lymphoid acute leukemias.