Continuity of contact between patients and physicians has become an important criterion of quality primary care. Using three measures of continuity that have appeared in the literature, this article examines, through the use of simulated data and through application to data from five primary care settings, the differences and utility of these approaches for measuring continuity. Further, these measures are applied to four selected diagnoses from each of the five sites, and the observed continuity scores afforded patients with these diagnoses are compared with those expected based on the population. Finally, the scores are correlated with the number of return visits prescribed and kept and with the rate at which laboratory studies are ordered. The findings indicate that site-specific differences in continuity prevail even after adjustments in the number of visits. Continuity based on selected diagnoses is greater, for the most part, than continuity afforded the patient population. Finally, continuity is related to the number of return visits prescribed but not to the number kept or the rate at which laboratory studies are ordered. The implications of continuity for other aspects of quality patient care are discussed.