Abstract: A system for delivering and implanting a radially expandable endoluminal prosthesis within a body lumen (e.g., blood vessel). The system comprises a) an introducer/dilator assembly, and b) a delivery catheter/loader assembly. The introducer/dilator assembly comprises an elongate tubular introducer sheath which may be provided with a valving assembly mounted on the proximal end thereof. Such valving assembly may incorporate i) a hemostatic valve, ii) a first sealing valve and iii) a second sealing valve, positioned in series, to prevent leakage of body fluid out of the proximal end of the introducer and to permit two or more elongate members (e.g., catheters, guidewires) having differing outer diameters to be inserted through the introducer without leakage of body fluid therefrom. A dilator, which has regionalized differences in stiffness, is initially deployable within the lumen of the introducer to facilitate advancement of the introducer to its desired location within the body.