OBJECTIVES: The objective of our work was to reduce, score, and validate the Accept questionnaire. METHODS: Accept is a 32-items PRO questionnaire measuring the concept of Acceptance. It was developed based on grounded theory and qualitative research. Each treatment characteristic was assessed on a response scale opposing “easy to accept” to “not easy to accept”. We conducted an observational prospective study on 182 subjects engaged in long-term treatment regimen. Adult patients where consecutively recruited by a network of pharmacists when prescribed with a drug indicated in various chronic diseases (including asthma, diabetes, various cardio-vascular diseases, retroviral infections, osteoporosis). Patients were asked to complete Accept and MMAS-4 questionnaires at Month 1, 3 and 6 after having given their informed consent. The structure was explored through PCA, and confirmed with multi-trait analysis. Internal consistency reliability of dimensions was assessed through Cronbach’s alpha. Scale-scale correlations were calculated. RESULTS: After reduction, Accept was made of 25 items organised in 1 overall Acceptance score and 6 domain-specific scores (efficacy, tolerance, convenience, constraints, treatment duration, multiple medication). Cronbach’s alpha was 0,85 for overall Acceptance score, which met convergent and divergent validity criteria (both 100%). The domain-specific scores showed satisfactory to good results (Cronbach's alpha ranging from 0,67 to 0,87, convegrent validity ranging from 63% to 100%, and divergent validity ranging from 33% to 100%). Scale-scale correlations ranged from 0.02 to 0.58, confirming the multi-dimensional nature of the questionnaire. The good properties of Accept were stable over time. CONCLUSIONS: Accept is a brief, comprehensive, generic questionnaire focused on Acceptance. Initial validation in a population of patients with a wide range of long-term treatment showed promising results and confirmed the position of Acceptance. Further, disease-specific, large prospective study are needed to assess the ability of Accept to predict persistence to treatment.