The relationship between the process of medical care and patient outcome is a central issue in health services research. We examined this relationship in 244 patients with adult-onset diabetes mellitus, who were under the care of private internists and family physicians. Process measures included physician awareness of patients' concerns, communication of information from physician to patient, medication-taking behavior, physician adherence to minimum care criteria, and extent of patient utilization of services. Outcomes measured during and after a 6-month follow-up period, included diabetic control status and patient satisfaction with medical care. Potentially confounding variables included practice and physician characteristics, patient demographic characteristics, and measures of disease severity. There was a small statistically significant correlation between physician awareness and control status, but the association was not maintained when controlling for other variables. Communication of information from physician to patient was significantly (p less than .005) associated with satisfaction in the multiple regression analysis but explained only 4 per cent of the variance in patient satisfaction. Thus, in patients under treatment for diabetes, there was little association between certain measures of care process and patient outcome. We suggest that process and outcome assessments are distinct but complementary aspects of quality of care.