OBJECTIVE : Pain catastrophizing is an important predictor of functioning and disability among individuals with chronic pain, and modification of catastrophic interpretations of pain is a proposed treatment mechanism of pain rehabilitation. The purpose of the current study is to examine the relationship between changes in catastrophic thinking and treatment outcomes for a large sample of patients with chronic pain. METHODS : 648 adult patients with chronic pain completed a 3-week intensive outpatient comprehensive pain rehabilitation program. Measures of pain severity, pain-related life interference, depression, and pain catastrophizing were completed at admission and discharge. RESULTS : Consistent with prior research, pain catastrophizing was associated with several negative pain-related outcomes. Results of a within-subjects mediational analysis indicated that pain catastrophizing not only improved during the treatment program, but also accounted for a significant portion of the variance in the reduction of pain severity, pain interference, and depression at the end of treatment. CONCLUSIONS : This study adds further support to the position that pain catastrophizing has a detrimental role in adaptation to chronic pain, and that this construct can be successfully modified in treatment to improve patient outcomes.