•Decentralized healthcare systems structure territorial borders within countries, fostering internal cross-border healthcare.•Historical, financial and political factors shape policy-makers’ engagement in cross-border healthcare.•Cross-border healthcare arrangements may become an arena for partisan competition.•Political and financial tensions hamper articulating effective responses to patient mobility in Spain. Cross-border patient mobility has become a topic of increasing interest for policy-makers and academic scholars. However, the focus on international dynamics hinders the fact that healthcare mobility takes place within national boundaries as well, particularly in countries characterized by decentralized health systems. This paper shifts the focus from the drivers of international patient mobility to the ones of policy-making on patient mobility within national borders, analyzing more than fifty policy arrangements adopted between Spanish Regions in the period 2000-2020. As the findings indicate, geographical/historical, economic and political factors are key to understanding the development of cross-border healthcare agreements, as well as the conflicts that may arise therefrom. Accordingly, these arrangements may become a controversial issue and a key arena for partisan competition, affecting the articulation of effective responses to patient mobility in Spain and, ultimately, patients’ rights.