Abstract: A vascular prosthesis may be implanted in a vessel, having substantially a T-shape, that includes a proximal tubular part forming the base of the “T” and a distal tubular part forming the head of the “T”. The second end portion of the distal tubular part is formed by a flap. The flap is opposed to a circumferential indentation in the deployed position. The structural frame of the flap includes an arched segment connected at its ends to the intermediate portion of the distal tubular part. The arched segment is bendable so as to form a joint for the folding/unfolding movement of the flap.