Introduction. The Western Ontario Shoulder Instability Index (WOSI) is a patient reported outcome measure to assess the impact of unstable shoulder on various spheres of a patient’s life. The aim of this paper is to present the stages of linguistic adaptation of the English version of the WOSI questionnaire into the Polish version (WOSI-PL). Material and methods. The research used the procedure of translation of research tools recommended by Mapi Research Institute, which allows to minimize errors resulting from the translation. Results. Two versions of the translation were created: A1V and A2V, and based on them, a common version BV was agreed. An English native speaker made a back translation version – BTV. Next, the BTV was compared with the source version SV, corrections were made and the CV version was created. Based on the analysis of experts’ assessments, a DV version was agreed, then evaluated by a group of 6 patients. The patients’ responses was analyzed, and the final version – WOSI-PL was created. Conclusion. The WOSI-PL constitutes a valuable tool to evaluate health-related quality of life in patients with shoulder instability. The questionnaire before being introduced to scientific research and clinical practice will be subjected to a validation process in order to evaluate psychometric properties.