OBJECTIVES: Shoulder pain is a prevalent reason in orthopedic clinic patients, with rotator cuff disorders being the most common cause. The Constant-murley Score (CMS) questionnaire is a practical and reliable tool for the assessment of shoulder joint function. METHODS: The CMS questionnaire was translated into Persian and completed by 57 patients with persistent shoulder pain due to rotator cuff tears (case group) and 50 healthy controls. The case group refilled the questionnaire after 7-10 days without receiving any special treatment. The reliability and validity of the questionnaire were measured via the test-retest method and known-groups validity with the t-test, respectively. The intraclass correlation coefficient (ICC) was calculated to estimate the agreement as a measure of test-retest reliability. RESULTS: The mean ages of the case (51.8±14.2) and control groups (52.0±10.0) were similar (P=0.94). No significant difference was found between the groups regarding co-existing clinical conditions (P=0.74). The mean CMS values of the case and control groups were 46.2 (±22.3) and 87.4 (±5.7), respectively, showing a statistically significant difference (P<
0.001). Moreover, the ICC was 0.95. CONCLUSION: The findings indicated that the Persian version of the CMS questionnaire was reliable (ICC=0.95) and valid (P<
0.001) for the assessment of shoulder pain and functional status in the Southern Iranian population with rotator cuff tear disorders.