Abstract: A guidewire having an elongated core having a radiopaque marker on a distal portion of the core and a plurality of indicia on the proximal extremity of the core to facilitate measurement of an intracorporeal location such as a stenotic region within a patient's coronary artery. The guidewire is first positioned within the patient with the distal radiopaque marker at one end of the intracorporeal location and an indicia representing a base reference point is noted on the proximal portion of the guidewire which extends out of the patient. The guidewire is then moved so that the distal radiopaque marker is located at or adjacent to the other end of the intracorporeal location and another indicia on the proximal portion of the guidewire adjacent to the reference point. The distance between the two indicia on the proximal extremity of the guidewire is a measurement of intracorporeal length.