OBJECTIVES: Despite numerous studies highlighting the importance of HbA1c control, literature quantifying the marginal effect of self-monitoring of blood glucose (SMBG) on HbA1c control is somewhat limited. Recognizing this knowledge gap, this study assessed the association between increased use of testing strips and glycemic control, taking into account insulin regimen, type I/II status, and other patient-level characteristics.  METHODS: Patient inclusion and exclusion criteria were adapted from HEDIS Comprehensive Diabetes Care guidelines. Commercially enrolled patients on insulin regimen (basal, bolus, or pre-mixed) with at least one diabetic strip fill between the ages of 18 to 75 years were identified from the HealthCore Integrated Research Database®. Continuous enrollment for 12 months pre/post the earliest testing strip fill (‘index’) was required. Clinical outcome was defined as most current HbA1c lab value within 1 year post-index period. Using average marginal effects (AME) analysis with bootstrapping, we estimated the likelihood of patient's control (HbA1c < 8.0%) as number of testing strip fills increased, adjusting for age, gender, insulin regimen, and other variables.  RESULTS: Within this population, 45.8% of patients were unable to achieve control rates of <8% during the study period.  However, patients with higher fill rates (>=4 fills) were more likely to achieve control (60.9%) relative to a 44.0% control rate among those with low fill rates (< 4 fills). Using the AME analysis, each increase in fills was associated with a 2.5% increase in achieving control (AME: 2.5%, 95% C.I.: 2.1% - 2.8%, p<.001). The marginal effect between strip fills and HbA1c control was greater among type I patients (AME: 3.5%, 95% C.I.: 2.5% – 3.5%, p<.001).   CONCLUSIONS: We found a statistically significant AME between testing strip fills and glucose control.  These findings highlight the importance of efforts to encourage better SMBG among patients on insulin, with implications for improved patient outcomes and long term cost savings.