Based upon a tripartite theoretical model of pain, the Pain Rating Index (PRI) of the McGill Pain Questionnaire (MPQ) continues to be one of the most frequently used instruments to measure clinical pain. Although a number of exploratory factor analytic studies have failed to consistently support the theoretical structure of the instrument, one previous confirmatory factor analytic study of chronic pain did statistically support the a priori model. Because it has been suggested that acute pain may not involve the same dimensions as chronic pain, this study provided a direct test of the theoretical structure of the MPQ through multi-sample confirmatory factor analysis (CFA) using data provided by women experiencing pain during labor (n = 185) and women experiencing acute postoperative pain (n = 192). Results of the LISREL CFA analysis indicated that the a priori, 3-factor, oblique model originally proposed by Melzack provided the most parsimonious representation of the data across the 2 samples of acute pain.