Nijmegen breakage syndrome is a rare autosomal recessive disorder characterized by a peculiar dysmorphic syndrome (microcephaly, "bird-like" facies, short stature), combined immunodeficiency with recurrent infections, X-ray hypersensitivity and predisposition to malignancy, mainly lymphomas, as a consequence of chromosome instability due to anomalies in the repair of double-stranded DNA breaks.We present a 6-year-old boy with Nijmegen breakage syndrome, who developed a large B-cell non-Hodgkin's lymphoma, localized in the lung without nodal involvement.