PURPOSE: Most published descriptions of organizations providing or improving quality of care concern large medical groups or systems; however, 90% of the medical care in the United States is provided by groups of no more than 20 physicians. We studied one such group to determine the organizational and cultural attributes that seem related to its achievements in care quality. METHODS: A 15-family physician medical group was identified from comparative public performance scores of 27 medical groups providing most of the primary care in our metropolitan area. Semistructured interviews were conducted with diverse personnel in this group, operations were observed, and written documents were reviewed. Four primary care physician researchers and a consultant then reviewed transcriptions, field notes, and materials during semistructured sessions to identify the main attributes of this group and their probable origins. RESULTS: This medical group ranked first in a composite measure of preventive services and fourth and sixth, respectively, in composite scores for coronary artery disease and diabetes care. Our analysis identified 12 attributes of this group that seemed to be associated with its good care quality, with patient-centeredness being the foundational attribute for most of the others. Historical factors important to most of these attributes included small size, physician ownership, and a high value on practice consistency among the clinicians in the group. CONCLUSIONS: The identified 12 attributes of this medical group seem to be associated with its superior care quality, and most of them might be replicable by other small groups if they choose to work toward that end.