Purpose: The present study was designed to carry out an Italian translation of the Constant–Murley Score (CMS-IT) and, subsequently, evaluate its reliability and validity. Methods: This study included adults diagnosed with any type of clinical shoulder dysfunction who could read and respond to the questionnaires. Those individuals who underwent surgeries of any kind on the affected shoulder during the previous 12 months and individuals with shoulder instabilities were excluded. All of the participants were evaluated by two operators, and the CMS-IT, Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire, and visual analog scale (VAS) were administered. The internal consistency was evaluated using Cronbach’s α , whereas the intra-rater and inter-rater reliabilities were evaluated using the intraclass correlation coefficient (ICC). The validity of the construction was evaluated using Pearson’s correlation coefficient between the scores of the administered scales. Results: A population of 72 individuals participated in this study. The internal consistency of the CMS-IT showed a value of 0.81. The ICC values showed that inter- and intra-rater reliability were 0.994 and 0.963, respectively. CMS-IT is inversely correlated with the VAS (−0.55) and DASH (−0.47) scales. Conclusions: This study revealed that the CMS-IT contained good internal consistency and good reliability. The results suggested that the CMS-IT questionnaire is a reliable and valid tool for assessing the shoulder dysfunctions of the Italian population, and it deserves broad applications in both clinical practice and research contexts. The scale can also be used as an alternative to the current “gold standard” VAS and DASH.