The invention is directed to adjustable length mold assemblies for forming inflatable members and methods for using adjustable length mold assemblies for forming inflatable members, such as, for example, balloons for use with balloon catheters and stent delivery systems. The adjustable length mold assemblies comprise at least two mold pieces adapted to fit together, one mold piece having a surface configured to be slidably received by a bore of the other mold piece, the placement of one piece within the other defining a chamber of variable length which forms the mold. Each adjustable length mold assembly of the present invention is effective to form balloons, where if desired different balloons formed by a single mold may have different lengths. The adjustable length mold assemblies may also comprise a positioner to put a mold piece in a desired position relative to the other, and a locking mechanism to secure a mold piece in a desired position.