Nijmegen breakage syndrome is a rare autosomal recessive condition, which belongs to the DNA repair disorders. The hallmarks of Nijmegen breakage syndrome are microcephaly, a typical facial appearance, growth retardation, immunodeficiency accompanied by recurrent infections, chromosomal instability, X-ray hypersensitivity, and predisposition to malignancy. Additional features include skin abnormalities, particularly café-au-lait spots and vitiligo, and congenital malformations, particularly clinodactyly and syndactyly. Psychomotor development is usually normal or only mildly to moderately retarded despite severe microcephaly. About three quarters of the Nijmegen breakage syndrome patients are microcephalic at birth and the remainders become microcephalic within the first year of life. Severe microcephaly at birth may be associated with normal mental development and counterwise. Life expectancy is reduced because of their tendency to develop malignancies at a relatively young age and sometimes fatal infections.