Objective: Several factors are known to impact response to the intensive interdisciplinary pain treatment (IIPT) program described in this study, yet no research has explored the role of perfectionism. This secondary data analysis explored direct and indirect relations between perfectionism and functional disability (primary outcome) and pain severity (secondary outcome) after IIPT, with pain catastrophizing and fear of pain as mediators.Methods: Youth (N = 253) aged 8-21 with chronic pain and associated disability completed pre- and post-IIPT measures of self-oriented perfectionism (SOP), socially prescribed perfectionism (SPP), pain catastrophizing, fear of pain, functional disability, and pain characteristics for routine clinical care and this nonrandomized trial. Eight mediated models were run for the two predictors, two mediators, and two outcomes.Results: Pretreatment perfectionism (SOP and SPP) led to greater reductions in pain catastrophizing over the course of IIPT, which resulted in lower pain severity (β = -.02 [CI = -0.07, -0.01] for SOP and β = -.02 [CI = -0.06, -0.003] for SPP) and less functional disability (β = -.06 [CI = -0.13, -0.01] for SOP and β = -.06 [CI = -0.14, -0.01] for SPP). Independent of pain catastrophizing, pretreatment SPP was directly associated with more posttreatment functional disability (β = .16 [CI = 0.05, 0.27]). Fear of pain was not a mediator.Conclusions: Findings suggest perfectionism has the potential to negatively impact IIPT outcomes. However, when perfectionistic youth with chronic pain learn to manage pain-related distress, they benefit. Results highlight the importance of assessing for and treating perfectionism and pain-related distress in youth with chronic pain. [ABSTRACT FROM AUTHOR]