OBJECTIVES: Coeliac disease is an autoimmune condition affecting approximately 1% of the population. The only treatment is a gluten-free diet, although research is underway to develop other treatments. Quality of life has predominantly been assessed using generic patient-reported outcome (PRO) measures. Two existing coeliac-specific PROs have limitations in terms of content validity. The aim of this study was to develop a new PRO for coeliac disease. METHODS: The Coeliac Disease Assessment Questionnaire (CDAQ) was developed through qualitative interviews with adults with coeliac disease (n=23), expert panels, cognitive interviews (n=10), a translatability assessment, and two surveys. Survey 1 determined the final items and structure of the CDAQ. Survey 2 evaluated test-retest reliability and construct validity. In survey 2, participants also completed the SF-36v2, and the CDAQ a second time after two weeks. RESULTS: Sixty-three candidate items were developed and refined to give 51 candidate items to include in survey 1 (response rate: n= 412, 52.0%). The final CDAQ contains 32 items in five domains: stigma (8 items); dietary burden (8 items); symptoms (5 items); social isolation (5 items); and worries and concerns (6 items). Domain scores and an overall index score can be calculated. Cronbach’s alpha values (internal consistency) ranged between 0.82 and 0.88 for all domains. Survey 2 (response rate: n=276, 34.5%) showed that CDAQ scores were more strongly correlated with the SF-36v2 mental health dimensions as had been expected. Of the 167 participants returning the follow-up CDAQ, 145 rated the impact of coeliac disease ‘about the same’ and were included in the test-retest analysis. Intraclass correlation coefficients ranged from 0.79-0.89. CONCLUSIONS: The CDAQ has been developed according to current best practice guidelines and is acceptable to patients, and displays good psychometric properties. It is intended for use in research and clinical practice. Assessment of responsiveness is currently underway.