OBJECTIVES:  To determine if 90-day fills at retail pharmacy are associated with greater adherence to medications included in the CMS Star quality measures. METHODS:  This observational cohort study includes new and established Medicare Part D (Med D) patients 18 years or older who had at least one prescription fill for any of the three CMS Star drug classes (diabetes, hypertension, or cholesterol) at Walgreens retail pharmacy in January 2016. Patients who filled their first Star drug prescription (index fill) with a 90-day supply are included in the 90-day group and all others are in the 30-day group. To minimize the differences between groups, we propensity score matched patients in the 90-day group, one-to-one, to patients in the 30-day group on age, gender, copay, comorbidities, and past medication adherence history. We evaluate two measures of medication adherence during the period from the index fill to the end of 2016: proportion of days covered (PDC) and optimal adherence (OA): the percent of patients with PDC≥ 80%. Student’s t-tests and Chi-square tests were used to evaluate differences in the 2 adherence measures. RESULTS:  The study cohorts consist of 41,704 diabetes patients, 90,034 hypertension patients, and 80,164 cholesterol patients. Average PDCs in all 3 Star drug classes were significantly (p <0.001) higher for the 90-day group than the 30-day group: diabetes: 82.44% vs. 75.84%, hypertension: 79.83% vs. 72.74%, and cholesterol: 77.09% vs. 70.45%. Percent of patients with PDC≥ 80% in all 3 Star drug classes were also significantly (p <0.001) higher for the 90-day group than the 30-day group: diabetes: 66.40% vs. 59.99%, hypertension: 60.22% vs. 53.98%, and cholesterol: 60.16% vs. 52.55%. CONCLUSIONS: When Med D patients start the calendar year with a Star drug class 90-day prescription at retail pharmacy they have significantly greater adherence measured in CMS Star ratings.