An introducer for an endoluminal prosthesis and a methods for delivering a prosthesis within a body vessel are described. The introducer comprises pusher catheter having a lumen extending therethrough, the lumen being in communication with an opening formed in the sidewall of the pusher. A sheath is disposed over the pusher catheter and also has an opening formed in its sidewall. The sheath is longitudinally movable relative to the pusher catheter between a prosthesis delivery position and a prosthesis deployment position. When the sheath is in the deployment position, the opening formed in the sidewall of the pusher catheter is at least partially longitudinally aligned with the opening formed in the sidewall of the sheath. A wire may extend though the opening in the sheath, the opening in the pusher, through the lumen of the pusher and through a fenestration in a prosthesis to cannulate a branch vessel.