Our objective was to evaluate 8 interpersonal and structural features of care as predictors of patients' voluntary disenrollment from their primary care physician's practice. We performed a longitudinal observational study in which participants completed a validated questionnaire at baseline (1996) and follow-up (1999). The questionnaire measured 4 elements of the quality of physician-patient relations (communication, interpersonal treatment, physician's knowledge of the patient, and patient trust) and 4 structural features of care (access, visit-based continuity, relationship duration, and integration of care). Study participants were insured adults who reported having a regular personal physician at baseline and who completed both baseline and follow-up questionnaires (n=4108). The outcome measured was voluntary disenrollment from the primary physician's practice between baseline and follow-up. One fifth of the patients voluntarily left their primary physician's practice during the study period. When tested independently, all 8 scales significantly predicted voluntary disenrollment (P <.001), with somewhat larger effects associated with the 4 relationship quality measures. In multivariable models, a composite relationship quality factor most strongly predicted voluntary disenrollment (odds ratio [OR]=1.6; P<.001), and the 2 continuity scales also significantly predicted disenrollment (OR=1.1; P<.05). Access and integration did not significantly predict disenrollment in the presence of these variables. These findings highlight the importance of relationship quality in determining patients' loyalty to a physician's practice. They suggest that in the race to the bottom line medical practices and health plans cannot afford to ignore that the essence of medical care involves the interaction of one human being with another.