A balloon catheter having a balloon with a shape for treating a vessel at a bifurcation, includes an oblique proximal end of the balloon, and a catheter shaft which is at least partially eccentric to a central axis of the balloon. Markers used for longitudinal and rotational alignment are included on the catheter shaft. A torque transmission element may be used for transmitting torque from the stiff proximal segment of the catheter to the distal flexible balloon segment of the catheter.