We report a patient with acute eosinophilic leukemia and a translocation (10;11)(p14;q21). Clinically, the disease was characterized by extreme hypereosinophilia with most eosinophils being immature, pronounced marrow infiltration with abnormal eosinophil precursors, skin and lymphoid infiltration with leukemic eosinophils, and only a brief remission from chemotherapy. This is the second report of a patient with this cytogenetic/clinicopathological association. In our patient, t(10;11)(p14;q21) was the sole karyotypic abnormality seen in the bone marrow, both at diagnosis and relapse. Thus, acute eosinophilic leukemia with t(10;11)(p14;q21) appears to be a rare, new clinical/cytogenetic association. Because both patients with this translocation responded only briefly to chemotherapy, this chromosomal abnormality may confer a poor prognosis.