Nijmegen breakage syndrome (NBS) is an autosomal recessive disorder, due to defects in the NBS1 gene and belongs to the DNA repair disorders. We report neuropathological findings of the first ever recognised case of the about 60 described cases of NBS. This patient showed severe microcephaly with a simplified gyral pattern especially in the frontal lobes. There were no signs of a degenerative disease, or of a primary migration disorder. A bulge on top of the corpus callosum, most probably a very large remnant of the involuting striae longitudinales mediales et laterales, was found. This can be considered as an incomplete development of limbic structures. The severe diminishment of neocortical neurones suggests an important role for the NBS1 gene in corticogenesis in man, as suggested earlier in animal studies of other DNA-repair genes.