An introducer sheath (10) is provided for percutaneous insertion of catheters into a blood vessel. The introduction of the sheath (10) through a wall of blood vessel causes an opening to be formed through which blood may pass from the blood vessel. The sheath(10) includes an inflatable collar (20) which may be expanded under pressurized inflation of fluid inserted within the inflatable collar (20) to expand into contiguous contact with a periphery of the opening formed by the sheath (10) to prevent blood leakage through the blood vessel wall opening.