This article systematically reviews published literature on different continuity of care (COC) indices that assess the physician-patient relationship and the applicability of such indices to pediatric and chronic-disease patient populations. Frequency and visit type may vary for pediatric and chronically ill patients versus healthy adult patients. Two investigators independently examined 5,070 candidate articles and identified 246 articles related to COC. Forty-four articles were identified that include 32 different indices used to measure COC. Indices were classified into those that calculated COC primarily based on duration of provider relationship (n=2), density of visits (n=17), dispersion of providers (n=8), sequence of providers (n=1), or subjective estimates (n=4). The diversity of COC indices reflect differences in how this measure is conceptualized. No index takes into account the visit type. A unique index that reflects continuity in the physician patient relationship for pediatric and chronic disease populations is needed.