A method of positioning a main stent at a vessel bifurcation includes positioning a main guidewire in the main vessel and advancing a stent delivery system to a position proximate the bifurcation. The stent delivery system includes a catheter with a flexible side sheath attached thereto and a main stent positioned over the catheter. The flexible side sheath is positioned to pass through the side opening in the main stent. The method also includes advancing a branch guidewire through the flexible side sheath and into the branch vessel and subsequently, advancing the catheter over the main guidewire while advancing the flexible side sheath over the branch guidewire while viewing relative movement of a marker positioned on the flexible side sheath with respect to at least one marker positioned on the catheter.
