Disclosed is an expandable transluminal sheath, for introduction into the body while in a first, small cross-sectional area configuration, and subsequent expansion of at least a part of the distal end of the sheath to a second, enlarged cross-sectional configuration. The sheath is configured for use in the vascular system and has utility in the introduction and removal of implant delivery catheters. The access route is through the femoral arteries and the iliac arteries into the aorta. The distal end of the sheath is maintained in the first, low cross-sectional configuration during advancement to the arteries into the aorta. The distal end of the sheath is subsequently expanded using a radial dilatation device, which is removed prior to the introduction of implant delivery catheters. In an exemplary application, the sheath includes a supported proximal end, a supported distal end, and a collapsible center section. Certain configurations of the sheath are capable of being inserted in a first, small cross-sectional configuration, being expanded diametrically to a second, larger cross-sectional configuration, and then being reduced to a diametrically small size for removal.