This study investigated the psychometric properties of the Chronic Pain Acceptance Questionnaire (CPAQ) in a mixed chronic pain, Internet sample and sought to develop a valid and reliable short form. Questionnaires were completed by 428 respondents, comprising a sample accessed via the Internet (n = 319) and a sample who completed a paper and pencil version of the measures (n = 109). Using confirmatory factor analysis (CFA) the two-factor structure of the CPAQ in the Internet sample was supported, though a good model fit was only achieved following the removal of one item. The resultant 19 item CPAQ demonstrated good reliability and evidence of validity was obtained for this sample. Data from the Internet sample were used to derive an eight-item short form. The two four-item factors (activity engagement [AE] and pain willingness [PW]) were confirmed using CFA and found to be invariant across both samples with good scale reliability. Higher CPAQ-8 and subscale scores were correlated with less depression and anxiety, pain severity and pain interference, and fewer medical visits for pain. Using structural equation modelling both subscales were found to partially mediate the impact of pain severity on pain interference and emotional distress. In this model AE had stronger associations with outcomes while PW accounted for a small portion of the variance in pain interference and anxiety, but not depression. This study confirmed the two-factor structure of the CPAQ in a mixed chronic pain Internet sample and provides preliminary evidence for the psychometric soundness of the CPAQ-8. (C) 2010 International Association for the Study of Pain. Published by Elsevier B. V. All rights reserved.