PURPOSE We wanted to undertake a critical review of the medical literature regarding the relationships between interpersonal continuity of care and the outcomes and cost of health care. METHODS A search of the MEDLINE database from 1966 through April 2002 was conducted by the primary author to find original English language articles focusing on interpersonal continuity of patient care. The articles were then screened to select those articles focusing on the relationship between interpersonal continuity and the outcome or cost of care. These articles were systematically reviewed and analyzed by both authors for study method, measurement technique, and quality of evidence. RESULTS Forty-one research articles reporting the results of 40 studies were identified that addressed the relationship between interpersonal continuity and care outcome. A total of 81 separate care outcomes were reported in these articles. Fifty-one outcomes were significantly improved and only 2 were significantly worse in association with interpersonal continuity. Twenty-two articles reported the results of 20 studies of the relationship between interpersonal continuity and cost. These studies reported significantly lower cost or utilization for 35 of 41 cost variables in association with interpersonal continuity. CONCLUSIONS Although the available literature reflects persistent methodologic problems, it is likely that a significant association exists between interpersonal continuity and improved preventive care and reduced hospitalization. Future research in this area should address more specific and measurable outcomes and more direct costs and should seek to define and measure interpersonal continuity more explicitly.