The effects of simulated clinical fabrication heat treatment and artificial weathering on the degree of crystallinity for three prosthetics/orthotics polymers were monitored by wide-angle x-ray diffraction. The polymers selected, polypropylene (PP), Subortholen (polyethylene, SB), and Surlyn (polyethylene methacrylate copolymer, SR), represent commonly used semicrystalline materials. Analysis of the as-received polypropylene showed no preferred orientation of the crystallites. The materials were examined in the as-received and simulated clinical fabrication heat-treated conditions. The simulated clinical fabrication heat-treated specimens were subsequently treated to 2 weeks, 4 weeks, and 8 weeks of artificial weathering conditions. The artificial weathering consisted of exposure to cycles of ultraviolet light and heated condensation. The degree of crystallinity was calculated and correlated with the materials structure, and ranged from 13.7 to 64.5% with an order from low to high of SR < SB < PP. The x-ray diffraction technique was demonstrated to be a useful tool for detecting environmental influences on prosthetics/orthotics polymers.