The expandable sheath and system (10) for intravascular insertion of a medical implement includes a cannula (70) for entering a lumen of a vascular vessel of a patient, a guide wire (72) insertable into the lumen, an introducer and dilator (62) adapted to follow the guide wire (72) into the lumen, an expandable sheath (40) positioned on the introducer and dilator (62), with the expandable sheath (40) being adapted to be positioned in the vessel, and an extension collar (76). The medical implement is received within the vessel by passing through the sheath (40) upon separating the introducer and dilator (62) therefrom. In one embodiment, a linear array of perforations (50) formed through the expandable sheath (40) allow for expansion. Alternatively, an external slit (16) may be provided for selective expansion of the sheath (40).
