A stent for supporting part of a blood vessel includes a supporting portion around which or within which part of an intact blood vessel, other than a graft, can be placed so that the stent internally or externally supports that part of the blood vessel. The supporting portion of the stent is of a shape and/or orientation whereby flow within the vessel is caused to follow a non-planar curve. By maintaining a non-planar curvature in the vessel itself, favorable blood flow velocity patterns can be achieved through the generation in the vessel of a swirl flow. Failures in such vessels through diseases such as thrombosis, atherosclerosis, intimal hyperplasia or through blockage, kinking or collapse, can be significantly reduced.