Measurement of glycosylated hemoglobin (HbA1c) among patients with diabetes mellitus contributes to attaining control of blood glucose, which in turn is associated with fewer complications. Here, we seek to identify physician and county level characteristics that predict increased HbA1c testing among Medicare beneficiaries with diabetes who did not have testing in the baseline year. Physicians in counties with more people on Medicaid, or with fewer physicians per capita tended to have less improvement in HbA1c testing among Medicare beneficiaries over the three year study period.