This research has used the technique of Social Network Analysis to analyze the structure of network relationships that surrounds on Twitter the three more important federations of associations of rare diseases and identify key actors in their communications. Methodology. NodeXL software has been used, with visualization as a key component, to capture the network of connections of the accounts under study, represent their interaction patterns and find out the position occupied by users within the network. Conclusions. The results indicate that these associations use social networks to raise awareness, educate and inform about RD and its problems. They are very influential accounts with a high degree of connection and a great capacity for prescription due to the interest aroused in a part of the population by these pathologies and everything that surrounds them.