The present invention relates to a multi-size catheter for use in biliary endoscopic procedures. The multi-size catheter comprises an outer diameter defined by a plurality of superimposed peelable layers. The peelable layers allow the multi-size catheter to function as a single operator exchange catheter without the need, and additional expense, of an endoscope sheath. Before positioning the multi-size catheter within the working channel of an endoscope, the peelable layers may be selectively removed in order to obtain an outer diameter for the catheter that is less than, but approximate to, the inner diameter of the working channel of the endoscope. The resulting fit eliminates the potential for a guidewire to slip out of the guidewire channel and become pinched between the catheter and the endoscope working channel. With an incorrect fit, a pinched guidewire would restrict the desired movements of both the guidewire and the catheter.