OBJECTIVE: To translate and assess the psychometric properties of the 9-item Shared Decision-Making Questionnaire (SDM-Q-9) for measuring patients' perceptions of how clinicians' performance fits the SDM process. DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: Data were collected in primary care health centres. Patients suffering from chronic diseases and facing a medical decision were included in the study. MEASUREMENTS: The original German SDM-Q-9 was translated to Spanish using the process of cross-cultural adaptation of self-reported measures as the methodological model for Spanish translation. Reliability (internal consistency) and construct validity [exploratory (EFA) and confirmatory factor analysis (CFA)] were assessed. RESULTS: The final Spanish version of the SDM-Q-9 was tested in a primary care sample of 540 patients. The SDM-Q-9 presented adequate reliability and acceptable validity. Internal consistency yielded a Cronbach's alpha of 0.885 for the whole scale. EFA showed a two-factorial solution, and for the CFA, the best solution was obtained with a one-dimensional factor with the item 1 excluded, which produced the best indexes of fit. DISCUSSION AND CONCLUSIONS: The Spanish version of the SDM-Q-9 showed adequate reliability and acceptable validity parameters among primary care patients. The SDM-Q-9 is suitable for use in Spain and other Spanish-speaking countries with similarly organized health-care systems. The use of the SDM-Q-9 may contribute to the evaluation of SDM process from the patient's perspective.