Continuity of care is a cornerstone of primary care that has been promoted by recent trends in medical education and in the way health care delivery is organized. We sought to determine the effect of sustained continuity of care (SCOC) on the quality of patient care.We conducted a systematic review of all articles in Medline (January 1966 to January 2002), Educational Resources Information Center (ERIC), and PSYCH INFO using the terms "continuity of care" or "continuity of patient care." We identified additional titles of candidate articles by reviewing the bibliographies of articles from our original MEDLINE search, contacting experts in primary care, health care management, and health services research, and by reviewing bibliographies of textbooks of primary care and public health.Two investigators (MDC, SHJ) independently reviewed the full text to exclude articles that did not fulfill search criteria. Articles excluded were those that focused on physicians-in-training, on SCOC in a non-primary care setting, such as an inpatient ward, or on transitions from inpatient to the outpatient setting. We also excluded articles that did not correlate SCOC to a quality of care measure.From 5070 candidate titles, we examined the full text of 260 articles and found 18 (12 cross-sectional studies, 5 cohort studies and 1 randomized controlled trial) that fulfilled our criteria. Five studies focused on patients with chronic illness (eg, asthma, diabetes).No studies documented negative effects of increased SCOC on quality of care. SCOC is associated with patient satisfaction (4 studies), decreased hospitalizations and emergency department visits (7 studies), and improved receipt of preventive services (5 studies).SCOC improves quality of care, and this association is consistently documented for patients with chronic conditions. Programs to promote SCOC may best maximize impact by focusing on populations with chronic conditions.