Little is known about the factors that predict the transition of acute, time limited pain to chronic pathological pain following postero-lateral thoracotomy. The aim of the present prospective, longitudinal study was to determine the extent to which (1) pre-operative pain intensity, pain disability, and post-traumatic stress symptoms (PTSS) predict post-thoracotomy pain disability 6 and 12 months later; and (2) if these variables, assessed at 6 months, predict 12 month pain disability. Fifty-four patients scheduled to undergo postero-lateral thoracotomy for intrathoracic malignancies were recruited before surgery and followed prospectively for one year. The incidence of chronic post-thoracotomy pain was 68.1% and 61.1% at the 6 and 12 month follow-ups, respectively. Multiple regression analyses showed that neither pre-operative factors nor acute movement-evoked post-operative pain predicted 6 or 12 month pain disability. However, concurrent pain intensity and emotional numbing, but not avoidance symptoms, made unique, significant contributions to the explanation of pain disability at each follow-up (total R(2)=76.3.0% and 63.9% at 6 and 12 months, respectively, both p<0.0009). The relative contribution of pain intensity decreased, while that of emotional numbing increased with time, indicating a progressive de-coupling of pain intensity and disability and a concomitant strengthening of the link between emotional numbing and disability. This suggests that pain may serve as a traumatic stressor which causes increased emotional numbing. The results also support recent suggestions that avoidance and emotional numbing constitute separate PTSS clusters. Further research is required to determine the source(s) of emotional numbing after postero-lateral thoracotomy and effective interventions.