Chromosomal rearrangements are described in a three-generation family whose members were all normal but for the propositus, who had phenotypic abnormalities suggestive of Patau’s syndrome. The rearrangements appeared to involve chromosomes of the D and E groups in four members of the family, and in the mother and the abnormal propositus, who had identical karyotypes, there was also a questionable abnormality of a B chromosome. Autoradiographic studies indicated that chromosomes 13 and 17 may be involved in the translocation and that the B-group abnormality involved possibly a chromosome No. 5. Genetic-marker studies were noncontributory. The explanation favored for the rearrangement was an insertion type of exchange following three breaks in the D and E groups, and hence the abnormal propositus could be explained as an example of recombinational imbalanc