OBJECTIVES: The National Quality Forum is a public organization that reviews, endorses, and recommends use of standardized healthcare quality measures, which are considered the gold standard in the United States. The NQF endorses a measure concerning medication adherence in patients with diabetes using sulfonylureas, thiazolidinediones or metformin. This study tests the performance of the diabetes adherence quality measure in the Mississippi Medicaid population. METHODS: Mississippi Medicaid administrative claims for calendar years 2008 to 2012 were used to assess the measure in the Mississippi Medicaid fee-for-service population. Eligible beneficiaries were at least 18 years of age, received at least two prescriptions in a specific therapeutic category and did not have any claims for insulin in the measurement period. The patient´s measurement period was defined as the period from the index prescription date to the end of the calendar year, disenrollment, or death. Adherence was defined as the number of covered days divided by total number of days in the measurement period.  RESULTS: The study population included had a higher proportion of females (approximately 75%), African-Americans (around 64%) and elderly (approximately 50%). Adherence to Sulfonylureas, Thiazolidinediones and Metformin was approximately 38%, 41% and 39% respectively in 2008. These numbers decreased steadily to about 26%, 35% and 26% respectively in 2012. CONCLUSIONS: Adherence to diabetes medications has been decreasing in the past few years. While this might reflect a need for greater adherence interventions, it is possible that these numbers are being caused by patients who are steadily moving from the fee-for-service plan to the managed care plan in Mississippi Medicaid. Nevertheless, adherence to diabetes medications is of critical importance to measuring quality of healthcare delivered. This study provides a valuable first look at the performance of this quality measure over several years in a Medicaid population.