We report the seventh case of Mulvihill-Smith progeria-like syndrome in a 5-year-old boy with a thin, pinched face, failure to thrive, and cutaneous pigmented nevi. The patient's motor and intellectual development were normal. His immune function tests demonstrate evidence of lymphopenia with no selective loss of a major subpopulation, low immunoglobulin (Ig)G2 and IgG4 subclasses, and an absent in vitro proliferative response to pokeweed mitogen. Chromosomal mitomycin and radiation sensitivity were normal. The skin fibroblast growth in culture was slow, and the fibroblasts appeared morphologically different from normal controls in their size and large number of inclusions. In addition, primary cilia, which normally issue from the centrosome, were absent-a new finding in fibroblasts in this disorder. It remains to be seen if the relative absence of centrosomal cilia in cultured fibroblasts in early passages is a consistent finding in this progeria syndrome.