OBJECTIVES: To reduce and validate the ADEOS questionnaire, an instrument specifically developed to evaluate treatment adherence by women with post-menopausal osteoporosis  METHODS: The ADEOS questionnaire has been developed with clinicians and patients. Before item reduction, it included 45 items covering 5 distinct themes related to adherence (personal characteristics, beliefs, perceptions, behaviour and information received). It was included for finalisation and validation in a cross-sectional observational study in French general practitioners. The study sample was randomly divided into 2 subsamples: one for item selection, one for validation. The item selection procedure was performed according to the association of the items with a generic measure of compliance, the Morisky Medication Adherence Scale (MMAS).  The validity of the score derived from these items was scrutinised by assessing its correlation with MMAS score. Its ability to separate compliant patients from non compliant patients according to MMAS was studied using area under receiver-operating characteristic curve (AUC). RESULTS: Five hundred sixty osteoporotic women were included, of whom 348 (62%) returned the ADEOS questionnaire. Patients who did not return the questionnaire were comparable to those who did in terms of demographics and medical parameters. The questionnaire quality of completion was very good, confirming its good acceptability. Twelve items of the questionnaire showed a statistically significant relationship (p<0.05) with the MMAS in the “item selection sample” (N=200) and were retained to derive the ADEOS score. In the “validation sample” (N=148), the ADEOS score was noticeably correlated with MMAS score (Spearman correlation coefficient: 0.58) and showed good discriminant validity according to MMAS (AUC: 0.84). CONCLUSIONS: The 12-item ADEOS questionnaire is a short validated instrument specific to osteoporosis, whose score can easily be calculated by hand. Therefore, it might be particularly useful in daily practice to detect patients at risk of being poorly adherent to their osteoporosis treatment.