Pentasomy 49,XXXXY occurs in 1/85,000 newborn males. The origin of this 
particular form of aneuploidy is believed to be a result of consecutive 
nondisjunction events during maternal meiosis. Typical presentation consists of 
hypotonia, developmental delay, various dysmorphic features, and severe 
hypogenitalism. A 13-year-old with pentasomy 49,XXXXY and a Chiari type 1 
malformation with an associated cervical syrinx is presented.