The KBG syndrome is a very rare condition characterized by developmental delay, short stature, distinct facial dysmorphism, macrodontia of the upper central incisors and skeletal abnormalities. Associated congenital heart defects have been described in 9% of patients. Herein is described a case of aortic root dilatation with significant regurgitation in a young patient affected by KBG syndrome. Surgical inspection showed a dilated aortic annulus, slightly dilated aortic sinuses, a tricuspid valvb with slightly thickened cuspal margins and central regurgitation. Histological examination showed a fibrous hyaline involution of the valvular leaflets. To the authors' knowledge, this is the first reported case of KBG syndrome affected by aortic root dilatation with severe regurgitation. Morphology of the aortic valve leaflets was relatively normal, but the annulus was dilated in the absence of any history of rheumatic fever, hypertension, connective tissue or rheumatic systemic diseases. The unusual findings in this young patient raised questions regarding the as-yet unexplained etiopathogenesis of the KBG syndrome.