Cytogenetic abnormalities of chromosome arm 9p occur frequently in children with acute lymphoblastic leukemia (ALL) . WE analyzed 201 such cases (11%) 1n 1839 children with newly diagnosed ALL . Patients with 9p abnormality had an increased cumulative incidence of both marrow (p=04) and central nervous system (p=0001) relapses . A 9p aberration was an adverse risk factor for B-lineage , but not T-lineage patients . The effect of 9p status on EFS was attenuated , but maintained in a multivariate analysis of EFS after adjustment for Philadelphia chromosome status , age , white blood cell (WBC) count , sex , race , and ploidy group (p=.01) Thus , abnormalities of chromosome arm 9p identify a subgroup . (Heerma et al ., 1999) .