Abstract: A size-adjustable high performance slip-on plastic roller skate has an injection-molded sole support piece in the form of separable front and rear sections respectively provided with wheel assemblies secured thereto. The sections are slidingly interfitted for movement toward and away from each other to vary the longitudinal extension of said sole support piece and can be locked at a plurality of the adjusted interfitted positions to enable accommodation of a plurality of shoe sizes. A metal reinforcing frame member is molded into one of said front and rear sections and extends within at least the interfitted portion of said sections, to bridge said portion at all size-adjusted positions, whereby to provide rigidity for the skate, enabling use of same in high performance applications.