Objective: To find the characteristics of diabetics with poorly controlled diabetes that became well controlled compared with the patients with poorly controlled diabetes that remained poorly controlled. Methods: The sample included diabetic patients, aged 40 years and older, from the Central district of Clalit Health Service in Israel, with at least one HbA1c measure greater than 9.5 mg% during 2001. They were divided into 2 categories according to their HbA1c levels in 2003, well controlled (HbA1c <7.5 mg%) and poorly controlled (HbA1c >9.5 mg%). Patients with 7.5< HbA1c <9.5 in 2003 were excluded from analysis. Results: Two thousand sixty-two diabetic patients met the inclusion criteria and care was provided by one of 249 primary care physicians. Of these patients, 1232 (41.6%) had well-controlled diabetes and 1760 (58.4%) had poorly controlled diabetes in 2003. The well-controlled group had fewer patients with low socioeconomic status (30.3% vs 41.9%; P < .001) and more men (52% vs 43.8%; P < .001). The individual primary care physician was the most significant predictor of good glycemic control. Total patient costs in 2004 were 8% lower among the group with well-controlled diabetes. Conclusion: The primary care physician has an important role in the patient's chances of achieving glycemic control. Further investigation of how and why some primary care physicians achieve better diabetes control in their patients would be worthwhile.