A guidewire having flexible or floppy proximal and distal end portions is used for percutaneously accessing a branch vessel through a deployed prosthesis having at least one fenestration near an ostium of the branch vessel. The prosthesis is delivered and deployed via a first percutaneous access site. The guidewire extends over the outside surface of the deployed prosthesis and extends through the at least one fenestration. The flexible distal end portion is snared via a second percutaneous access site and is pulled in a direction towards the second percutaneous access site until the flexible proximal end of the guidewire is located adjacent to the branch vessel. A guide catheter is then advanced over the guidewire until it cannulates the branch vessel. The flexible proximal end of the guidewire may then be advanced into the branch vessel and used for delivery of a branch vessel prosthesis.
