An endoluminal graft includes a unitary tube of graft material forming two adjacent legs that are integral and monolithic to each other. The graft can be part of a prosthesis assembly for treatment of branched vascular systems and can function as an integral bifurcated leg extension prosthesis in combination with a main bifurcated prosthesis. In treating abdominal aortic aneurysms, the graft can be deployed within both iliac arteries.