A catheter having optical fibers for delivering laser energy to a blood vessel to remove obstructions in the blood vessel is adapted to be guided controllably and selectively by a guide wire to the site to be treated. The catheter includes a central lumen which is open at the distal end of the catheter and which receives the guide wire so that the catheter may be advanced over the guide wire. A relatively few number of optical fibers are contained within and extend longitudinally of the catheter wall. The distal tip of the catheter is provided with a cylindrical optically transparent end cap and means are provided to securely mount the distal ends of the optical fibers with respect to the end cap so that the light emitted from the ends of the fibers passes through the cylindrical wall of the end cap and is emitted at the distal emissions face of the end cap. The catheter embodies a special construction of an inner catheter core and a surrounding sheath which provides for a high degree of flexibility to enable the catheter to be passed through tortuous passages in a patient's vasculature. The inner core is formed from a plurality of articulated segments and is surrounded by a thin flexible sheath. Longitudinal flutes formed along the articulated segments of the core receive and retain the optical fibers in a manner which permits the fibers, sheath and core to shift longitudinally with respect to each other to provide a very high degree of flexibility for the composition catheter.