Abstract: Apparatus for inserting an instrument (1) in a flexible body cavity is disclosed. The apparatus includes a sheath (3) having an inner chamber (31) for accommodating the instrument (1) and an outer chamber (41) surrounding the inner chamber, thereby defining an enclosed space between the inner chamber and the outer chamber Fluid pressure is temporarily applied to thse enclosed space so as to expand the outer chamber to facilitate insertion of the instrument in the body cavity. In another embodiment the inner chamber is expandable to have a diameter equal to or greater than the diameter of the outer chamber, and wherein the outer chamber incorporates one or more lines of weakness for facilitating release and expansion of the inner chamber and withdrawal of the instrument from the inner chamber. In yet another embodiment the sheath includes at its distal end a convex lens for use by a camera in obtaining images of said body cavity.