Evidence-based medicine enables the profession to resist at least some of the challenges to its traditional autonomy: if informed doctors provide what is scientifically proven to be the best care there is less justification for external constraints. Yet, this defensive strategy depends on enforcing a new discipline within the profession such that individual practitioners accept mechanisms of external 'decision support' in their clinical practice. A study of the ways in which general practitioners in British Primary Care change their clinical behaviour shows that an emphasis on a 'patient centred' approach establishes an alternative individualised autonomy that seems inimical to the logic of evidence-based medicine. A tension therefore emerges between the maintenance of the autonomy of the profession as a collectivity through the promotion of a therapeutic rationality and the maintenance of the autonomy of the individual practitioner through the rhetoric of patient-centredness.