OBJETIVES: ARTS is a self reported instrument designed to measure four treatment satisfaction dimensions: Treatment advantages, Treatment convenience, Apprehension about treatment and Satisfaction with medical care; and is composed by 18 Likert-scale items. It is intended to be used with patients suffering osteoarthritis and undergoing oral administered treatments. METHODS: Linguistic adaptation was performed using the standard processes for establishing conceptual equivalence. A panel of six experts supervised the process and four independent translators translated and back-translated the items. A sample of 163 patients was used to gauge psychometric properties. All patients suffered from knee, hip or column arthritis. Patients were included in 3 groups: treatment-switch because of a weak analgesic effect, treatment-switch due to poor tolerability and no-change. The ARTS was administered at baseline,1 week later and after 4 weeks of therapy with traditional NSAIDs or Cox II-inhibitors. RESULTS: Mean age was 67.7 ± 9.2 years old. The adapted instrument showed good feasibility and reliability properties. No floor or ceiling effects where found, items where well understood and non-response rates were below one percent (1%). Cronbach's alpha for the total scales was 0.85. Instrument was stable with a test-retest intraclass correlation coefficient of 0.83. Exploratory factor analysis yielded four dimensions coherent with those proposed by the original authors. Convergent validity was measured against SF-36, a pain VAS a treatment compliance VAS, and Morisky-Green compliance questionnaire. The adapted instrument showed good discriminant validity, being able to distinguish between patients needing a change in treatment and those which didn't need it. It also showed to be sensitive to changes in patients' treatment effectiveness after a 30 days follow up. CONCLUSIONS: A psychometrically valid and conceptually equivalent version of the ARTS questionnaire has been produced to explore satisfaction with treatment in patients with osteoarthritis in Spanish speaking countries.