Résumé : We report on two cases, one with acute lymphoblastic leukemia and a second with lymphatic blastic phase of Philadelphia chromosome-positive chronic myelogenous leukemia, cytogenetically characterized by ider(9)(q10)t(9;22)(q34;q11). Our findings and the data of the 4 cases previously published indicate that ider(9)(q10)t(9;22)(q34;q11) represents a rare but recurrent chromosomal abnormality occurring in hematological malignancies with lymphoid differentiation, namely acute lymphoblastic leukemia and lymphatic blastic phase of chronic myelogenous leukemia, and most likely evolves from a preexistent der(9) involved in the standard t(9;22).