A catheter assembly adapted to treat a vessel bifurcation. A balloon member of the catheter assembly includes a main body portion and a cylindrical shaped bulge portion that extends radially outward from the main body portion. The bulge portion extends around a circumference of the main body portion. A stent of the catheter assembly is typically mounted to the balloon member. When treating the vessel bifurcation, the catheter assembly is positioned with the bulge portion aligned axially relative to an ostium of the branch vessel. The balloon member is inflated to expand a portion of the stent into the branch vessel. The circumferential construction of the bulge portion of the balloon member reduces the need for radial (rotational) alignment of the balloon member relative to the ostium of the branch vessel.
