The present study evaluated the relative importance of different cognitive factors (anxiety sensitivity and trauma-related beliefs) in predicting PTSD symptom severity and treatment-related changes in these symptoms. Eighty-one victims of motor vehicle accidents (MVAs) completed self-report measures of PTSD symptoms, anxiety sensitivity (AS), MVA-related beliefs and control variables (e.g., medication use, pain severity). A subsample of patients (n=28), who received cognitive-behavioural treatment for PTSD, completed these measures pre- and post-treatment. For the combined sample (n=81), regression analyses indicated that AS and pain severity were significant predictors of PTSD symptoms, whereas MVA-related beliefs were not. For patients completing treatment, regression analyses indicated that reductions in AS and pain severity were significant predictors of reductions in PTSD symptoms. MVA-related beliefs did not significantly predict symptom reduction once AS, pain severity and medication status was controlled for. These findings suggest that AS is a significant cognitive risk factor for exacerbating and maintaining PTSD symptoms. Treatment implications are discussed.