The national welfare state, so it seems, has come under attack by European integration. This article focuses on one facet of the welfare state, that is, health care and on one specific dimension, that is, cross-border movement of patients. The institution which has played a pivotal role in the development of the framework regulating the migration of patients is the European Court of Justice (ECJ). The Court’s activity in this sensitive area has not remained without critics. This was even more so since the Court invoked Treaty (primary) law which not only has made it difficult to overturn case law but also has left the legislator with very little room for manoeuvre in relation to any future (secondary) EU law. What is therefore of special interest in terms of legitimacy is the legal reasoning by which the Court has made its contribution to the development of this framework. This article is a re-appraisal of the legal development in this field.