We report on a 30-year-old woman with premature aging, immunodeficiency, and other abnormalities. She had many manifestations of the Mulvihill-Smith syndrome, a disorder that has been described in 4 sporadic individuals, ranging in age from 4 to 17 years. The common manifestations include short stature, microcephaly, a senile face with an underdeveloped lower half, diminished facial subcutaneous fat, multiple pigmented nevi, sensorineural hearing loss, and a low IgG level. Our patient also had severe mental retardation, brachydactyly, severe T cell dysfunction, and suffered from severe verruca vulgaris and a chronic, active Epstein-Barr virus infection. The fact that her parents were first cousins suggests autosomal recessive inheritance of her disorder. Two alternative possibilities were considered: the disorder in the patient represents the Mulvihill-Smith syndrome with immune deficiency as a sign of its advanced stage, or a hitherto undescribed syndrome.