A balloon catheter or stent delivery system for medical treatment of a patient has a proximal hub (12), a balloon (16), and a shaft (14). The catheter shaft has a rapid-exchange configuration, and a tubular outer body (24) that includes a hypotube (48) extending from the catheter proximal end to a position at or near a proximal leg of the balloon. An inner tubular body (26) defines a guidewire lumen extending from a distal guidewire port (30) at the catheter distal end to a proximal port (18) located at a position between the balloon and the hub The hypotube has an aperture for accepting the inner body proximal end, and a circumferential cut pattern. The cut pattern adds flexibility, and may extend from the hypotube distal end to a position proximal of the proximal guidewire port
