A chromosomal translocation between chromosomes 4 and 8 resulting in Wolf-Hirschhorn syndrome in 2 individuals has been traced through 4 generations of a family. Ascertainment of the family was through a newborn infant with evident Wolf-Hirschhorn syndrome who had an unbalanced chromosomal translocation [46,XY,-4,+der(4),t(4;8) (p15.32;p22)]. Discussion with the family documented a paternal great-uncle who also had a similar phenotype and profound mental retardation. Subsequently this individual was found to have the same unbalanced chromosome constitution as the propositus. The 39-year-old great-uncle is the oldest reported individual with the Wolf-Hirschhorn syndrome. The importance of chromosome evaluation of older individuals with mental retardation syndromes is emphasized.