The ANSI Y14.5M Geometric Dimensioning and Tolerancing Standards have been used for many years by practitioners for size and form verification of manufactured parts. However, different parts may satisfy these tolerances and yet perform quite differently because of surface variations not specified in the standards. We present a statistically-based technique for the determination of the type of surface variation for cylindrical parts. This technique is based on a parametric-based part representation used for fitting. The method is illustrated with examples. [S1087-1357(00)00403-2]