OBJECTIVE: To demonstrate that one physician can dramatically improve care of diabetes patients by taking a systems approach and getting support from leaders and other team members. MATERIAL AND METHODS: Pre-/postcomparison of quality measures for the diabetes patients of one primary care physician, compared with those of his entire large multi-specialty medical group. Working with a mentor and with clinic and medical group leaders, he established a clear goal, focused on a repeatable and important performance measure, and used repeated rapid cycle trials to make systems changes in care, with extensive task delegation to team members and emphasis on repeated testing and treatment intensification. The composite outcome measure requires that each diabetes patient meet all 5 of the following: LDL <100, HbA(1C) <7, systolic blood pressure <130, regular aspirin use, and tobacco-free status. RESULTS: Over a 24-month period, quarterly measures for this physician's patients rose from 5.7% to 42.9%, while the 7000 diabetes patients of the entire medical group only increased from 4.2% to 12.1%. The change for those patients who stayed under his care for the entire period was even more dramatic-from 2.3% to 46.5% (P = <.0001). The largest improvements were for smoking documentation, aspirin use, and LDL control, with little change in HbA(1C) levels. CONCLUSION: One physician can accomplish a lot, if improvement is approached both systematically and persistently and if the work is coordinated with and supported by practice leaders.