Disclosed is an ostial stent positioner that has the form of a wire for most of its length and having a short cylinder with a longitudinal slit and expandable legs situated at the positioner's distal end. The slit cylinder with its attached wire acts as an introducer sheath to introduce a stent delivery system with a stent into the artery that is to be stented. A second aspect of the present invention is a method for accurately placing a stent at the ostium of an artery that would have an ostial stenosis. Examples of such arteries that have ostial stenoses are the right and left main coronary arteries, a saphenous vein graft as used in coronary bypass surgery and the renal arteries. Also disclosed are designs for the slit cylinder that provides a variable diameter so as to fit snugly within guiding catheters having different inside diameters.