Background <p>Rare diseases (RDs) present complex challenges, including diagnostic uncertainty, limited treatment options, and fragmented research and care systems. These constraints contribute to inequities in access to care, information, and research participation among patients and caregivers across social and institutional contexts. In this setting, rare disease patient advocacy groups (RDPAGs) have emerged as key actors, not only providing support to patients and caregivers but also increasingly engaging in research. However, empirical evidence regarding their research engagement and organisational capacities remains limited, particularly in Central and Eastern Europe. This study examines the engagement of RDPAGs in research and intersectoral collaboration in Poland.</p> Methods <p>A cross-sectional survey was conducted between January and April 2026 among representatives of 64 Polish RDPAGs using a structured, web-based questionnaire. The questionnaire covered organisational characteristics, research engagement, collaboration, and perceived barriers. Data were analysed using descriptive statistics.</p> Results <p>Most RDPAGs reported at least occasional engagement in research, although involvement was heterogeneous and often limited in scope. RDPAGs were primarily active in non-clinical research domains, including social research, patient registries, and dissemination of research findings. Participation in clinical and translational research was less frequent and largely supportive, particularly in recruitment and patient support. A majority of RDPAGs did not initiate research activities, and only a small proportion reported high levels of engagement. Key barriers included a lack of funding, limited human resources, and restricted influence on research processes. Despite these constraints, collaboration with physicians was common, although often informal. The findings indicate that RDPAGs function as intermediary actors and knowledge brokers, partially compensating for structural gaps in healthcare and research systems by facilitating access to information, support, and research participation for patients and caregivers. The findings further suggest a model of constrained co-production, in which RDPAGs participate in research but remain insufficiently integrated into research decision-making and knowledge production.</p> Conclusions <p>RDPAGs play an important but structurally constrained role in research and knowledge co-production. Strengthening their contribution requires formalised collaboration frameworks, improved access to resources, capacity-building initiatives, and earlier and more meaningful involvement across the research cycle. Enhancing their role may contribute to more inclusive and effective research systems in the rare disease field.</p> Clinical trial number <p>Not applicable.</p>