Angio-osteohypertrophic (AOH) syndrome is a congenital vascular bone syndrome characterised by the presence of vascular malformations in a limb resulting in limb overgrowth. Depending on whether the malformations are slow flow venous or fast flow arteriovenous the syndrome may be divided into two subtypes, Klippel-Trénaunay and Parkes-Weber syndromes respectively. Some cases of the latter are associated with mutations in the RASA1 gene.