An endoluminal prosthesis comprising: a tubular body comprising a biocompatible graft material and having a proximal end, a distal end, an anterior side, and a posterior side; at least a first fenestration and a second fenestration in the graft material, the first and second fenestrations being spaced from one another circumferentially around the tubular body and being located at substantially the same longitudinal position; and at least one first diameter reducing tie positioned circumferentially on the posterior side of the prosthesis directly between the first and second fenestrations and engaging at least a circumferential segment of the posterior side of the tubular body, the engaged segment of the posterior side being restrained from expansion by the first diameter reducing tie; the prosthesis being characterised in that at least one second diameter reducing tie is positioned circumferentially directly between the first and second fenestrations on the anterior side of the prosthesis and engaging at least a circumferential segment of the anterior side of the tubular body, the engaged segment of the anterior side being restrained from expansion by the second diameter reducing tie, wherein at least a portion of the prosthesis is movable between a reduced diameter configuration and an expanded configuration, an angular position of the first fenestration in the expanded configuration is substantially the same as the angular position of the first fenestration in the reduced diameter configuration, and an angular position of the second fenestration in the expanded configuration is substantially the same as the angular position of the second fenestration in the reduced diameter configuration. a tubular body comprising a biocompatible graft material and having a proximal end, a distal end, an anterior side, and a posterior side; at least a first fenestration and a second fenestration in the graft material, the first and second fenestrations being spaced from one another circumferentially around the tubular body and being located at substantially the same longitudinal position; and at least one first diameter reducing tie positioned circumferentially on the posterior side of the prosthesis directly between the first and second fenestrations and engaging at least a circumferential segment of the posterior side of the tubular body, the engaged segment of the posterior side being restrained from expansion by the first diameter reducing tie; the prosthesis being characterised in that at least one second diameter reducing tie is positioned circumferentially directly between the first and second fenestrations on the anterior side of the prosthesis and engaging at least a circumferential segment of the anterior side of the tubular body, the engaged segment of the anterior side being restrained from expansion by the second diameter reducing tie, wherein at least a portion of the prosthesis is movable between a reduced diameter configuration and an expanded configuration, an angular position of the first fenestration in the expanded configuration is substantially the same as the angular position of the first fenestration in the reduced diameter configuration, and an angular position of the second fenestration in the expanded configuration is substantially the same as the angular position of the second fenestration in the reduced diameter configuration.