The objective of this study was to determine the frequency content of the surface bumpiness in shapes encountered in prosthetic and orthotic practice. This information is important in evaluating digitizers for use in prosthetic and orthotic CAD/CAM; a digitizer's frequency response should be capable of recording the intricacies of a limb's shape without degradation. A digitizing system without adequate frequency response has results analogous to a loudspeaker that muffles high frequency notes.Of the shapes commonly encountered, below-knee (BK) residua were found to have surface undulations of the highest frequency. Fifty-five BK limbs were digitized, and evaluated to determine the spatial frequency spectra of the surface. Shapes with known frequencies were also tested, in order to ensure proper performance of the algorithm. The frequency content of the BK limbs was limited to 10 cycles per circumference or lower.