Nijmegen breakage syndrome (NBS) is a rare autosomal recessive disease (8q21) from the family of the genetically determined chromosomal instability syndromes. The disorder is characterized by microcephaly, growth retardation, immunodeficiency, and high incidence of cancer. Several noninflammatory anomalies of the musculoskeletal system have been described in patients with this syndrome. We describe an Argentinian girl with all the clinical, immunological, and cytogenic characteristics described for NBS plus a juvenile rheumatoid arthritis-like syndrome. To our knowledge this is the first report of a patient with the NBS who presented with a symmetric chronic polyarthritis resembling JRA.