Continuity of relationship between physician and patient is a fundamental aspect of the health care provided by family physicians. Measurement of continuity has proved difficult, however. Commonly applied measures, usual provider of care (UPC), continuity of care (COC), and the modified continuity index (MCI), either ignore key aspects of continuity or provide misleading results. Consequently, a new measure of continuity, the modified, modified continuity index (MMCI), with a possible range of 0 to 1, was developed to overcome these problems. It was applied to a residency model practice, in which mean MMCI was found to be 0.59 (range 0.3 to 1.0). Mean COC was .41 and a mean MCI was .44. Thus, unlike COC and MCI, MMCI suggests fairly good continuity of care in this practice while still implying possible improvement. The MMCI should be useful for enhancing training and practice of family medicine.