Continuity of care with a personal health care provider is both an honored and controversial concept. This paper reviews the literature regarding the effect of a continuous relationship with a personal health care provider (longitudinal care) on quality of care using specific selection criteria and methodological standards. Sixteen studies were found of which four provided most of the valid information. Among the studies reviewed, the most common serious methodological problem was inconsistent definitions of continuity. Longitudinal care from a provider has been shown in certain settings to improve patient and staff satisfaction, compliance with medication and with appointments, and patient disclosure of behavioral problems. No ill effects have yet been demonstrated. There is some evidence that having an ongoing provider could reduce the costs of care. From available information, any evolution of the medical care delivery system away from reliance on an ongoing relationship between provider and patient may sacrifice important benefits.