A pericentric inversion of a group D chromosome was found in a phenotypically normal nine-year-old boy in the course of a chromosome survey of children with behavioral disorders. Family studies demonstrated its presence in eight other individuals, all of whom were also phenotypically normal. Autoradiographic studies suggested that the inversion involved the No. 15 chromosome. Evaluation of 17 gene markers failed to establish linkage of their genetic loci to the inverted No. 15 chromosome.