Advantage90TM allows patients to get maintenance medications in 90-day supplies from a network of retail pharmacies. Before the introduction of this program, medications in 90-day supplies can only be purchased through mail. OBJECTIVES: This study evaluated the impact of the program on prescription drug costs and generic utilization. METHODS: Using pre-post cohort study design, prescription records were obtained from Walgreens Health Initiatives' pharmacy claims database. For the purpose of this study, specialty drugs were excluded. Clients were selected if they had 3-tier formulary design and no mandatory mail program, were rebate-eligible and continuously enrolled. The study group comprised of 236,950 eligible lives from 17 clients enrolled in Advantage90TM during January 1, 2004 and May 1, 2004, and the control group included 282,116 lives from 84 clients not enrolled in the program. The pre and post periods were defined as 8 months from the enrollment date. Per member per month (PMPM) total costs and generic utilization were analysed. RESULTS: There were no statistically significant difference between the study and control group in terms of client type, client region, and whether clients were enrolled in the retrospective drug utilization review and other clinical programs. From the pre to post period, in Advantage90TM group, PMPM total costs and the percentage of generic utilization among eligible members increased by 1.93% (from $32.57 to $33.20) and 9.5% (from 40.1% to 43.9%). In the control group, PMPM total costs and the percentage of generic drug utilization increased by 5.62% (from $36.30 to $38.34) and 7.9% (from 39.3% to 42.4%). Advantage90TM was estimated to have resulted in a PMPM total cost savings of $1.20. CONCLUSIONS: A 90-day retail program like Advantage90TM led to decreases in PMPM total costs and increases in generic utilization on maintenance medications and can be an effective option to lower drug costs.