We report the clinical, hematological and immunophenotypic characteristics from four cases of acute leukemia with interstitial deletion of chromosome 9, ie del(9)(q12-q22), as a single chromosomal abnormality. Three patients had acute myeloblastic leukemia (AML) and one T origin acute lymphoblastic leukemia (ALL). According to FAB classification, blasts were classified as M1 (two patients), M2 (one patient), and L2 (one patient). In two out of three AML cases a myelodysplastic syndrome, one AREB-t and one AREB diagnosed 6 and 11 months before respectively, preceded the onset of AML. Morphological examination showed dysgranulopoiesis, dyserythropoiesis and cytoplasmic vacuoles in two AML patients, while a strong positivity to myeloperoxidases was observed in all AML cases. As concerns immunophenotypic findings, blast cells from two of three AML patients expressed CD7 and CD34, while those from the T-ALL case displayed CD33 and CD34 along with CD7. These observations suggest that del (9q) is associated with CD7+ acute leukemia of myeloid or lymphoid lineage.