Measurement of depression and other mood states in pain patients has been criticised in recent years on the grounds that most questionnaires were not developed in pain populations and suffer from criterion contamination by somatic items. In addition, there is no accepted measurement for positive emotions which are more than the absence of depression. The aim of this study was to develop a reliable and brief tool to assess mood in pain patients. Non-somatic items concerning depression, anxiety and positive outlook were extracted using exploratory factor analysis from commonly used instruments (the Beck Depression Inventory and the Hospital Anxiety and Depression Scale) completed by over 900 chronic pain patients. Confirmatory factor analysis was used to test the internal structure of the final item set. Items were then reworded and presented as a new questionnaire (the Depression, Anxiety and Positive Outlook Scale: DAPOS) to two new samples: patients attending pain management and patients attending osteopathy. The new questionnaire was compared with several well-known questionnaires (SF36, BDI, PCS). The structure was calibrated and tested using confirmatory factor analysis on both samples. Finally, a subset of patients carried out a sorting task to test for face validity. The DAPOS performed well, indicating that it is a reliable measure of the three mood states with good initial evidence of validity in these samples.