Nine related individuals have been identified as being trisomic for the distal part of the long arm of chromosome 15 (15q23 to 15qter). The physical characteristics, especially the facial features, of these nine cases are similar and distinctive. These include: facial asymmetry, down-slanting palpebral fissures, ptosis, prominent nose, long philtrum, down-turned mouth, midline crease in the lower lip, puffy cheeks, and micrognathia. By comparing related individuals with the same translocation, the variability due to different breakpoints can be eliminated. Clinical similarities between unrelated individuals with similar duplicated 15q material, but differing second chromosomes, suggest that the phenotype is due to the extra distal 15q chromosomal material. We conclude that distal 15q trisomy produces a clinically recognizable syndrome.