Germ-line mutations of the BRCA2 gene (13q12-13) account for a large proportion of familial breast cancer cases in females and the majority of familial breast cancers in males. Recent studies provide evidence for a role of the BRCA2 protein in the maintenance of genomic integrity by involvement in DNA repair and recombination. In pursuit of identifying in humans genetic damage resulting from mutated BRCA2, we have analyzed constitutional karyotypes of BRCA2 mutation carriers. The present study establishes that constitutional distal 9p rearrangements without obvious additional gross chromosomal alterations are a recurrent feature of independently ascertained families. From our cytogenetic analyses we have no indication of additional gross rearrangements, but we cannot exclude more subtle recombinations in other genomic regions. We also show that the topography of the 9p rearrangements can differ among family members, even within an individual that can have cell populations with different 9p rearrangements. Collectively these results raise point to an association of mutant BRCA2 with genomic instability and gene alteration in 9p23-24 in at least a subset of BRCA2 mutation carriers.