We report on a family with 4 affected males in 3 generations with a previously unreported X-linked mental retardation/multiple congenital anomaly (XLMR/MCA) syndrome. The propositus was a 7-year-old Latin American moderately retarded male with: prenatal and postnatal overgrowth; short, broad upturned nose; large mouth; midline groove of tongue, lower alveolar ridge and lower lip; submucous cleft palate; supernumerary nipples; 13 ribs; Meckel's diverticulum; intestinal malrotation; coccygeal skin tag and bony appendage; hypoplastic index fingernails; postaxial polydactyly of the right hand, bilateral syndactyly of 2nd and 3rd fingers; and tibial clinodactyly of 2nd toes. His sister's son, a premature infant who died at 4 months, had nearly identical manifestations. The propositus and his nephew had normal chromosomes. A brother and son of the sister of the mother of the propositus were similarly affected and both died in the newborn period. The mother of the propositus had a large mouth, coccygeal skin tag and bony appendage, and hypoplastic index fingernails. This distinct mental retardation/multiple congenital anomaly syndrome is added to the growing list of presently known X-linked MCA/MR syndromes.