A constraining sheath for use around an endoprosthesis (e.g., a stent device, with or without a graft covering), which may be a balloon expandable endoprosthesis but more preferably is a self-expanding prosthesis. The endoprosthesis is coaxially enclosed within and substantially covered by the constraining sheath, which is an outer, removable tubular sheath, preferably made of ePTFE. The sheath is preferably corrugated circumferentially along at least a portion of the length of the endoprosthesis. The constraining sheath and endoprosthesis are preferably mounted together as an assembly at the distal end of a delivery means such as a catheter shaft, for delivery of the endoprosthesis to a desired location within a body conduit such as an artery. The constraining sheath is removed by the application of tension to a tensile member such as a tether to cause sequential pulling out of the corrugations followed by release and deployment of the endoprosthesis. The use of a corrugated constraining sheath in comparison to a non-corrugated sheath results in a more smoothly applied tensile force to effect the endoprosthesis release as well as requiring less maximum force.