A prosthesis consisting of a flexible thin-walled sleeve for reinforcing and repairing a damaged vessel and a process of placing the flexible sleeve in the vessel by collapsing the sleeve radially onto an expandable and contractable member and encasing the member and sleeve in a sheath; and then sliding the sleeve in place in a vessel covering the damaged area of the vessel and removing the sheath; then expanding the expandable member and the sleeve so that the sleeve covers the damaged area and forms a sealed interface on its outer peripheral ends with the inner peripheral surface of the vessel to thereby provide a bridging passage across the damaged area in the vessel. The device provides a process to reinforce or repair weakened, damaged, narrowed blood vessels or to divert flow in branching vessels. The sleeve is a flexible, plastic, thin-walled sleeve molded with various types of ribs and reinforcements to be used as an endovascular prosthesis. It also includes a means of delivering the prosthesis to the damaged blood vessel without surgery. With the device a physician may patch the inside of a blood vessel without performing an arteriotomy and without the use of an operating room and other facilities. A patch is placed within a vessel endovascularly preventing further expansion of the blood vessel, preventing leakage of the blood from the vessel wall and preventing or treating narrowing of the blood vessel, eliminating blood flow into a branching vessel from the abnormal region.