Background: In 2010, Tuscany (Italy) implemented the Chronic Care Model (CCM), to improve general practitioner (GP) management of chronic diseases. Aim: assessing how the introduction of CCM affected GPs’ compliance with standards of care for diabetes patients. Methods: A controlled before-after study was performed. Two exposed groups of GPs, one entering the study in 2010 and one in 2011, were considered. Patients with diabetes assisted by GPs of the groups were identified through the healthcare administrative data of the Regional Healthcare System and followed up from 2009 to 2012. A diabetes care indicator called Guideline Composite Indicator (GCI: annual assessment of glycated haemoglobin and at least two assessment among eye examinations, total serum cholesterol, and microalbuminuria) and an indicator of adherence to statin therapy were computed per year and by group. Impact of intervention was estimated by difference in differences analysis for panel data, stratified by GP performance level at baseline. Results: 483 GPs constituting the first group entered the study in 2010, 258 GPs of the second group entered it in 2011, and 1,820 GPs constituted the control group. After 1 year, the diabetes care indicator increased of 8.1%. During the second year, it showed a further increase of 1.6%. The mean impact on the adherence to statin therapy was smaller (+1%), yet statistically significant. Conclusion: The first year of the CCM implementation had a significant impact on the diabetes care indicator, and performance was stabilized after the first year. Impact on therapy indicator was smaller.