The Nijmegen Breakage Syndrome (NBS) is a rare chromosomal instability disorder clinically characterized by microcephaly, typical facial appearance, growth and mental retardation, immunodeficiency and a significant predisposition to lymphoid malignancy. The gene mutated in NBS, NBS1, has been mapped to the 8q21 chromosome. The product of this gene is a protein with a molecular weight of 95 kDa named nibrin. One of the common features of NBS is dysregulation of both cellular and humoral arms of the immune system, resulting in recurrent bacterial and viral infections, mainly of the respiratory tract. NBS is a rare syndrome. It should be considered that NBS may be associated with immunodeficiency.