We report 5 new cases of the FG syndrome, 1 sporadic, 3 brothers from a European family, and another affected male born in the first FG syndrome family reported by Opitz and Kaveggia in 1974. The pedigree data confirm the hypothesis of X-linked inheritance of this multiple congenital anomaly/mental retardation (MCA/MR) syndrome. Its manifestations include shortness of stature with a disproportionately large head, mental retardation, hypotonia with or without congenital joint contractures, seizures and a strikingly characteristic personality of facial appearance, imperforate anus and/or orthe gastrointestinal defects, congenital heart defects, and many minor manifestations. Chronic pulmonary disease in some affected males may be a complication of hypotonia.