Introduction and objective:
Rare disease patient organizations (RDPOs) contribute to improving access to healthcare, medicines, psychosocial support, and social services for people living with rare diseases (RD). Limited evidence exists on how they develop their organizational identity and how this influences their patterns of collective action. The study examines how RDPOs organize activities and how disease affiliation shapes organizational identity, culture, and strategy.

Material and methods:
A qualitative study design was adopted. Data were collected over a 3-year period through non-participant observation, 20 interviews with Polish RDPOs, and documents review followed by reflexive thematic analysis. Methodological triangulation was applied to enhance study credibility.

Results:
RDPOs comprise small and homogeneous communities of patients and caregivers, facilitating alignment between activities and community needs. Organizational identity is grounded in affiliation with a specific RD, distinguishing them from other NGOs, shaping their functional model. RD affiliation provides basis for collaboration at home and promotes participation in international networks. Advances in medical knowledge accompany increasing organizational specialization, reflected in the growing number of organizations representing single RDs. This pattern has been observed for over 20 years in Poland and the EU

Conclusions:
RDPOs constitute a key healthcare component, supporting advocacy, public education, R&D, and collaboration with policy stakeholders. Disease-specific identity and community homogeneity facilitate relationship-based networks at both national and international levels. These findings suggest that collaboration, rather than competition, characterizes their organizational development and shapes policies strengthening patient participation in health systems.