A catheter assembly especially designed for the performance of atherectomy procedures which includes a guide catheter having an inflatable balloon disposed on the distal end portion thereof, the guide catheter being dimensioned to receive in its lumen an elongated drive tube having an annular cutting tip affixed to the distal end thereof. A rotational drive mechanism is coupled to the drive tube at its proximal end for rotating same. Provision is also made in the drive mechanism for introducing fluid through the lumen of the guide catheter for inflating its balloon and for drawing a vacuum on the lumen of the drive tube for aspirating the treatment site. In use, the guide catheter with the drive tube and cutter head retracted is advanced up to the occlusion and then, the balloon is inflated to lock the distal end in place. Next, the cutter is rotated at high speed and advanced into the occlusion, while blood and any loose particulate matter is aspirated. The balloon is then deflated and advanced further into the lesion. These steps are repeated until the balloon is totally across the occlusion.