A balloon geometry is utilized herein where the balloon is inflatable from an initial unexpanded state to an expanded state. The balloon includes first and second portions; the first portion having a first diameter with the balloon being in the expanded state, the second portion having a second diameter with the balloon being in the expanded state, the first diameter being different from the second diameter. With a stent being mounted onto the balloon, expansion of the balloon results in the first portion of the balloon assisting a first portion of the stent to radially expand more than a second portion of the stent located adjacent to the second portion of the balloon. Preferably, the stent is formed of shape memory polymer. With the subject invention, one or both ends of the stent can be formed with larger diameters, or flares, in vivo at the point of implantation. The flared ends provide engagement points for the stent to a surrounding bodily passageway. Although the balloon may have various applications, it is particularly well-suited for use with shape memory polymer stents, which can be expanded and deformed in vivo.