In 1994, the Institute of Medicine (IOM) convened the Committee on the Future of Primary Care to provide a clearer understanding of the essential and desirable attributes of primary care. Perhaps the committee's most striking addition to the IOM's 1978 definition was the concept that primary care includes a sustained partnership with patients. Development of the partnership is considered an explicit responsibility of the primary care clinician. Although there is an extensive and growing body of literature on the effects of clinician-patient communication on outcomes such as patient satisfaction, adherence, symptom abatement, and physiological measures of health status, the impact of a sustained partnership in a clinician-patient relationship remains largely unstudied. There is also no consensus regarding either the definition or achievement of a sustained partnership. This paper reviews selected relevant literature and proposes a theoretical basis for assessing the existence, antecedents, and outcomes of sustained partnerships between clinicians and patients. At a time when there is increased discussion and clarification of optimal clinician and patient roles in a rapidly evolving health care delivery system, we believe this mode can provide guidance to clinicians and provider organizations seeking to improve the quality of primary care.