As a principle of healthcare planning, continuity of care is losing ground. It is increasingly being superseded by other principles—notably, accessibility and plurality of provision. Baker1 has identified the pressures and Hjortdahl2 writes of continuity ‘going out of style’. National Health Service (NHS) walk-in centres provide open-access primary care on sites separate from general practices and staffed by different people. For the first time, it is possible that continuity of care will be phased out of NHS planning. If this happens, what will be the consequences for patients and doctors? Over many years a research group in Exeter, including all the authors of this paper, has been developing a theory of continuity, based partly on clinical experience and partly on published evidence. The essence of the Exeter theory is that, in primary care, a ‘personal doctor’ with accumulating knowledge of the patient's history, values, hopes and fears will provide better care than a similarly qualified doctor who lacks such knowledge; and that the benefits of such continuity will include not only greater satisfaction for the patient but also more efficient consultations, better preventive care and lower costs. When we assess continuity in primary care, the duration of registration with the general practitioner (GP) is only one background factor. A more important consideration is the total time the patient and doctor have been in direct communication; and this will include contacts about third parties, such as a child, or an elderly relative during a home visit. We recognize that continuity can have disadvantages; for example, a fresh eye may see what the familiar eye has missed. In this paper we examine the published evidence for and against continuity in primary care.