A stent graft has a tubular body of a biocompatible material and at least one fenestration. A tubular side branch is stitched into the fenestration with a portion of the side branch extending within the tubular body and a portion of the side branch extending exteriorly of the tubular body. The stitching by which the side branch is mounted into the fenestration extends circumferentially and diagonally from one end of the side branch to the other such that the side branch extends from the tubular body at an angle thereto. The tubular side branch may have a reinforcement stent having at least one helical wire segment.