OBJECTIVES: Pharmacists play an integral role in quality improvement programs through medication therapy management services (MTM). This study estimates the effect of a pharmacist-led and delivered MTM program on achieving Optimal Diabetes Care (ODC). METHODS:  The study included patients with diabetes who received MTM services at Fairview Clinics during a 2007 demonstration project (n= 121) and those invited to receive MTM services but opted out (n= 103). Baseline characteristics were compared between the two groups. Rates of ODC for 2006, 2007 and 2008 were compared using McNemar’s test based on Minnesota Community Measurement all-or-none 5-component (D5) ODC measure (HbA1c <7%; LDL<100mg/dl; blood pressure<140/90mmHg; tobacco free; and daily aspirin use). Linear and Nonlinear multivariate difference-in-differences (DID) estimation were used to evaluate the impact of one-year exposure to MTM on each component of D5 ODC measure. RESULTS: The MTM group had more co-morbidities, more complex medication regimens and a higher percentage of diabetes with complications (p<0.05). There was significant improvement in ODC rates for the MTM group in 2007 compared to 2006 (45.45% vs.21.49%, p <0.001) and a significant decline in 2008 (45.45% vs. 25.62%, p=0.0002). The control group showed a significant improvement in 2007 compared to 2006 (39.81% vs.24.27%, p=0.0002) and a non-significant decline in 2008 (39.81% vs. 30.10%, p=0.077). Non-Linear DID models showed that MTM patients were more likely to meet the HbA1c criterion in 2007 (OR: 2.48, 95% CI: 1.04-5.85, p=0.038). Linear DID models for HbA1c showed a mean reduction of 0.54% (95% CI: 0.091%-0.98%, p=0.018) for MTM patients. Among MTM patients, rates of meeting HbA1c criterion in 2008 declined to baseline values. CONCLUSIONS: Despite their greater complexity, optimal diabetes care significantly improved among patients who were exposed to MTM. Drop in optimal HbA1c control after discontinuation of MTM exposure highlights the importance of regular access to MTM services.