Myelodysplastic syndrome (MDS) is a clonal hematopoietic stem cell disorder characterized by ineffective hematopoiesis, peripheral cytopenia, and dysplastic changes in the bone marrow. Monosomy 7 or partial loss of 7q is a common cytogenetic abnormality in MDS patients and is associated with poor prognosis. This study examined eight patients with monosomy 7 and MDS. Five MDS patients with monosomy 7 progressed to acute leukemia: three cases transformed into acute myelogenous leukemia (AML) in a mean time of only 4.6 months and two cases into acute lymphoblastic leukemia (ALL) in a mean time of 9 months. To our knowledge, this is the first report showing progression of monosomy 7 associated with MDS to ALL in the childhood period. (c) 2006 Elsevier Inc. All rights reserved.