OBJECTIVES: To develop a multidimensional specific questionnaire of factors related to weight loss therapies proposed for the assessment of therapy success or failure. METHODS: Three focus groups of patients where debriefed and an expert panel gathered relevant issues and converted them into 54 items around 9 dimensions: Alimentary Habits, Expectations towards Therapy, Effort and Concern, Emotion, Confidence, Believes, Motivation towards Physical Exercise, Motivation towards Weight Loss, and Perceived Control. Comprehension and legibility were questioned in a pilot sample. A first item reduction was done to avoid redundancies and to establish content agreement. Item reduction was carried out in a sample of patients using factor analysis. Feasibility, reliability, content validity and factor validity were assessed. RESULTS: A panel of 11 practitioners and researchers, belonging to different health centers in the Community of Madrid gathered 3 samples: One sample of 8 chronic patients participating in 3 focus groups; a sample of 8 patients to assess feasibility; a sample of 121 patients for item reduction. A first conceptual reduction conveyed a 32 item version. After measurement in a representative sample a final 17 items form was accepted. Items were arranged around 6 dimensions: Impulsiveness, External Locus of Control, Internal Locus of Control, Emotiveness, Motivation towards Therapy and Exercise, and Personal Image. Overall Cronbach's a was 0.772 (ICC 95% confidence interval = 0.698-0.835). The 6 dimensions solution accounted for 71.2% of variance, with all eigenvalues above 1. CONCLUSIONS: The new questionnaire is a very short inventory of factors which might have screening properties in order to forecast the efficacy of weight loss therapies. Although further prospective research is being carried out in order to assess predictive validity, basic psychometric properties are good as a baseline model. Resulting dimensions are meaningful and well formed.