OBJECTIVES: Medication non-adherence is a complex phenomenon that requires tailored interventions to improve it. A new self-reported measure of medication non-adherence was developed based on the commonly reported reasons underlying non-adherence. The goal of the new scale was to match the items in the scale with tailored interventions. The objectives of this study were to revise the original Medication Adherence Reasons Scale (MAR-Scale) based on expert opinion and cognitive interviewing and establish the psychometric properties of the scale. METHODS: A cross sectional design was used in collaboration with the Intermountain Medical Center Outpatient clinic for cholesterol lowering (CLM) and asthma maintenance medications (AMM). The study was conducted in two phases: Phase 1 - the original MAR-Scale was revised based on expert opinion and cognitive interviewing, Phase 2 - the revised MAR-Scale was tested for psychometric properties in a random sample of 350 subjects each on CLM and AMM. RESULTS: Revisions were made based on expert opinion that included asking a global question about adherence in the past 7 days, simplifying the items and converting them into first person sentences, objective anchoring of the scale, and expanding the “forgetfulness” item. Cognitive interviewing added one additional item to the survey. The MAR- Scale identified 48% of the CLM respondents and 65% of the AMM respondents as non-adherents. An exploratory factor analysis identified four domains in each medication with Cronbach alpha ranging from 0.848 to 0.953 in CLM and 0.827 to 0.891 in AMM. For validity, the scale exhibited significant correlations (0.434 for CLM and 0.539 for AMM at p<0.01) with the well validated Morisky scale and also had significant negative correlation with self-efficacy (-0.226 for CLM and -0.329 for AMM at p <0.01). CONCLUSIONS: The study resulted in a revised MAR-Scale that demonstrated better psychometric properties than the original scale.