The COSMIN guideline for systematic reviews of patient-reported outcome measures (PROMs) aims to provide a comprehensive and standardized methodology for conducting such reviews. The guideline is developed based on literature reviews, expert opinions, and existing guidelines, and it consists of a ten-step procedure. The first four steps focus on preparing and performing the literature search and selecting relevant studies. Steps 5-8 involve evaluating the quality of eligible studies, measurement properties, and interpretability and feasibility aspects. Steps 9 and 10 address formulating recommendations and reporting the systematic review. The guideline emphasizes the importance of combining the methodological quality of studies on measurement properties with the quality of the PROM itself, enabling reviewers to draw transparent conclusions and make evidence-based recommendations. The COSMIN guideline is designed to support the selection of high-quality PROMs for research and clinical practice, addressing gaps in knowledge and improving the overall quality of systematic reviews of PROMs.The COSMIN guideline for systematic reviews of patient-reported outcome measures (PROMs) aims to provide a comprehensive and standardized methodology for conducting such reviews. The guideline is developed based on literature reviews, expert opinions, and existing guidelines, and it consists of a ten-step procedure. The first four steps focus on preparing and performing the literature search and selecting relevant studies. Steps 5-8 involve evaluating the quality of eligible studies, measurement properties, and interpretability and feasibility aspects. Steps 9 and 10 address formulating recommendations and reporting the systematic review. The guideline emphasizes the importance of combining the methodological quality of studies on measurement properties with the quality of the PROM itself, enabling reviewers to draw transparent conclusions and make evidence-based recommendations. The COSMIN guideline is designed to support the selection of high-quality PROMs for research and clinical practice, addressing gaps in knowledge and improving the overall quality of systematic reviews of PROMs.