A cell culture was established from a skin biopsy of a 6 1/2 yr old male with cri-du-chat syndrome, characterized by physical and mental retardation, striking feeble cry resembling mewing of a cat, microcephaly, hypotonia and hypotelorism. His cells in culture have 45 chromosomes, including 2 translocations. In all cells the long arm of chromosome 15 is translocated to the short arm of chromosome 5 at 5p14. A deletion of 5p14 to 5pter has occurred either by loss of a small reciprocal translocation product or prior to the translocation. In addition, 50% of the cells have a translocation of the distal tip of the long arm of chromosome 11 to the short arm of chromosome 9. This culture, with a chromosome complement of 45,XY,del(5)(pter.fwdarw.p14:),t(5;15)(5qter.fwdarw.5p14::15q1.fwdarw.15pter),t(9;11)(9qter.fwdarw.9p24::11q23.fwdarw.11qter)(11pter.fwdarw.11q23::9p24.fwdarw.9pter), is potentially useful to demonstrate linkage relationships with chromosomes 5, 15, 9, and 11. Both parents and a normal female sibling have normal karyotypes.