Chronic pain is a potentially stigmatizing condition. However, stigma has received limited empirical investigation in people with chronic pain. Therefore, we examined the psychometric properties of a self-report questionnaire of stigma in people with chronic pain attending interdisciplinary treatment. Secondarily, we undertook an exploratory examination of the magnitude of change in stigma associated with interdisciplinary treatment in a prospective observational cohort. Participants attending interdisciplinary treatment based on Acceptance and Commitment Therapy completed the Stigma Scale for Chronic Illness eight-item version (SSCI-8; previously developed and validated in neurological samples), and measures of perceived injustice, pain acceptance, and standard pain outcomes before (n=300) and after treatment (n=247). A unidimensional factor structure and good internal consistency were found for the SSCI-8. Total SSCI-8 scores were correlated with pain intensity, indices of functioning, and depression in bivariate analyses. Stigma scores were uniquely associated with functioning and depression in multiple regression analyses controlling for demographic factors, pain intensity, pain acceptance, and perceived injustice at baseline. SSCI-8 total scores did not significantly improve following treatment, although an exploratory subscale analysis showed a small improvement on internalized stigma. In contrast, scores on perceived injustice, pain acceptance, and pain outcomes improved significantly. Taken together, these data support the reliability and validity of the SSCI-8 for use in samples with chronic pain. Further research is needed optimise interventions to target stigma at both the individual and societal levels. Perspective: This study supports the use of the SSCI-8 to measure stigma in chronic pain. Stigma is uniquely associated with worse depression and pain-related disability. Research is needed to identify how to best target pain-related stigma from individual and societal perspectives.