Abstract The role of the national judiciary in enforcing EC law, and particularly European Court of Justice (ECJ) rulings, has been largely neglected by empirical legal and political science research. Existing research has categorised the role of the national judiciary as either shielding national legislation from the ECJ or as serving as a sword to foster integration and to force change on reluctant governments. This article sides with the second assumption and attempts to empirically assess it using the example of the patient mobility jurisprudence by the ECJ, the so-called Kohll/Decker jurisprudence. The three case studies on France, the UK and Germany show that national courts played an important role in overcoming the resistance against this jurisprudence: via a multiplication of national court cases that contradicted domestic legislation they forced the legislator to end judicial uncertainty.