OBJECTIVES: Chronic obstructive pulmonary disease (COPD) is one of the most common lung diseases.  COPD prevalence among US adults was estimated to be 15 million or 6.3 percent of the total population in 2011.  Nonadherence to COPD maintenance medications has been reported to be associated with more hospitalizations, higher mortality and lower quality of life.  This study examined COPD maintenance medication adherence among Medicare beneficiaries with COPD. METHODS: An observational, retrospective cohort study was conducted using 2007 and 2008 Medicare Current Beneficiary Survey (MCBS) data.  Sample inclusion criteria were being diagnosed with COPD and having at least two Medicare Part D claims.  Medication adherence was measured by calculating proportion of days covered (PDC).  PDC was calculated as the number of days with COPD maintenance medications available divided by total number of days in a six-month period following index dates, which were defined as the date of first COPD maintenance medication fill in 2007.  A dichotomous variable was used to determine adherence status.  Individuals with PDCs of 0.80 or greater were considered adherent and individuals with PDCs less than 0.80 were considered nonadherent.  Logistic regressions were used to examine associations between demographic variables and medication adherence. RESULTS: A total of 292 beneficiaries fulfilled sample selection criteria and were included in the analysis. The mean age was 72 years, 54 percent were ≤ 75 years old and 11 percent were 85 years or older.  The sample was predominantly female (60%) and white (85%). The mean±standard deviation PDC was 0.69±0.24.  More than half (59%) of the Medicare beneficiaries had PDC of less than 0.80 and were classified as nonadherent to their COPD maintenance medications.  No significant differences were found in adherence across age groups (p=0.34), genders (p=0.43), or races (p=0.62). CONCLUSIONS: Adherence to COPD maintenance medications was low among Medicare beneficiaries with COPD.