Central nervous system (CNS) involvement is an independent risk factor for poor event-free survival and relapse confined to the CNS. Knock-out mice deprived of RAG2, the protein involved in DNA repair, developed leukemic infiltration within leptomeninges. Therefore, we hypothesized that DNA repair deficiencies in humans, such as Nijmegen breakage syndrome (NBS), may constitute a risk factor for CNS dissemination of acute lymphoblastic leukemia (ALL). Having analyzed the incidence of CNS2/CNS3 status at diagnosis of ALL in two independent cohorts from the Polish Pediatric Leukemia/Lymphoma Study Group, we noticed that among children with NBS CNS involvement was significantly frequent. Pediatr Blood Cancer 2011;57:160–162. © 2011 Wiley-Liss, Inc.