The development and use of validated processes of change (POC) measures have received little attention in the literature despite their importance in the Transtheoretical Model. Using survey data (N = 2909), we examined the construct validity of a 22-item mammography POC scale by testing for factorial validity and factorial invariance across stage of change. We also used MANOVA with Tukey post-hoc tests to confirm stage differences in POC use (concurrent validity). Our results confirm the a priori correlated four-factor structure of this scale and provide some support for the measurement equivalence of this scale across stage, supporting comparisons of POC use across stage.