A 37-year-old patient with back pain and somatomegaly was found to have a penetrating aneurysm of sections IV and V of the abdominal aorta. Results of a family history and clinical examination confirmed suspicions of Marfan's syndrome. Further angiologic studies depicted an aneurysmatic dilatation of the left popliteal artery. Aneurysmatic dilatations are primarily located in sections I and II of the thoracic aorta, whereas aneurysms in sections IV and V are much rarer. The rare combination of an abdominal aortic aneurysm and left-sided popliteal aneurysm accompanying Marfan's syndrome is presented.