OBJECTIVES: The 4-item Morisky Medication Adherence Scale (MMAS-4) and more recent 8-item version (MMAS-8) have both been validated and demonstrate concurrent validity among patients with hypertension, but the extent to which the scales can be compared has received little attention. This study assessed the comparability of adherence scores obtained with these scales in patients with type 2 diabetes (T2D) as well as the feasibility of integrating results across the scales using 4 items of the MMAS-8. METHODS: Data were taken from the 2011 and 2012 US National Health and Wellness Survey (NHWS).  The NHWS is a large cross-sectional survey representative of the total adult population in several major markets; N~75,000/year in the US. A total of 13,007 respondents self-reported physician diagnosis of T2D and were administered MMAS-4 in 2011 or MMAS-8 in 2012. The two adherence scales were evaluated by comparing the frequency distributions of the MMAS scores for the two scales, Cronbach’s alpha and inter-item correlations, and the creation of a new 4-item scale including the questions in MMAS-8 that best matched the questions in MMAS-4. RESULTS: In T2D patients, both MMAS-4 and -8 scores are Poisson-like distributed, with median at zero (high adherence) for MMAS-4 and at 1 (medium adherence) for MMAS-8. Chronbach’s alpha was 0.55 for MMAS-4 and 0.71 for MMAS-8, while average item-test correlations were 0.65 and 0.57, respectively.  The reduced 4-item scale created out of MMAS-8 is also Poisson-like distributed, Cronbach’s alpha was 0.62 and the average item-test correlation was 0.68. CONCLUSIONS: Scores of the two MMAS show similar qualitative and quantitative characteristics, suggesting that it may be appropriate to integrate data sources using the two different versions, particularly when the responses to the subset of 4 MMAS-8 items are available.  Future research should confirm that the scales can be integrated in different therapeutic areas.