Pain acceptance contributes significantly to the effectiveness of pain treatment outcomes. Nevertheless, little research has been conducted to examine whether a decrease in acceptance contributes to a deterioration in post treatment functioning. The aim of this study was to assess the role of pain acceptance in relation to process and outcome variables in the six-months following the conclusion of a pain program. Adults with chronic pain (N = 120) completed assessments at the completion of a 3-week multidisciplinary treatment program and 6-months post-treatment. Process measures included the Chronic Pain Acceptance Questionnaire-8 (CPAQ-8); the catastrophizing scale of the Pain Response Self-Statement Scale; the coping cognitions scale of the Pain Response Self-Statement Scale; and the Tampa Scale of Kinesiophobia. Outcome measures included the Roland Morris Disability Questionnaire; the depression scale of the Depression Anxiety and Stress Scale; and two measures of physical functioning. Deterioration in acceptance of pain was significantly associated with deterioration in depression and disability, even when catastrophizing cognitions and kinesiophobia were accounted for. Decrease in acceptance was the strongest predictor of reliable deterioration in depression and disability. Results indicated the CPAQ-8 has utility as a measure for monitoring patient functioning post-treatment.