Over the past decade, the recognition and diagnosis of rare diseases have increased, leading to a wealth of knowledge within specialised clinical teams, particularly within the European Reference Networks (ERN). These networks connect over 1,600 teams from more than 300 hospitals across the EU/EEA. The current challenge is to turn this expertise into real-world evidence that improves diagnosis, care and treatment. This involves developing disease-specific outcome measures to assess the effectiveness of care, enabling knowledge-sharing among experts. ERKNet and Endo-ERN showcased practical examples of such measures, their development, implementation, and the pivotal role of patient representatives in improving diagnosis, care, and treatment.