A retractor (101) for retracting the margins of a wound opening (103) comprises an inner anchoring O-ring (105) attached to a cylindrical sleeve (106) at a distal end and a reinforcing O-ring (109) attached to a proximal end of the sleeve (106). The sleeve (106) is led between an inner ring part (110) and a corresponding recess (116) in an outer ring part (111). The outer ring part (111) has anchor formations (120) over which the proximal end of the sleeve (106) is attached to anchor the sleeve (106). To retract the wound opening (103) the sleeve (106) is pulled while the guide rings (110, 111) are moved against the tissue surrounding the wound opening (103). This pulls the inner O-ring (105) against the inside of the tissue adjacent the wound opening (103), and retracts the wound opening (103). The sleeve (106) is manipulated locally for maximum retraction efficiency.