OBJECTIVES: To evaluate the impact of a 90-day retail program on prescription drug expenditures in a pharmacy benefit management organization. METHODS: This study was based on prescription records from pharmacy claims database for a time period from January 1, 2003 to August 31, 2005. A retrospective cohort study design with one-year pre period and one-year post period was employed. Propensity scores were used to match the study and control clients in terms of patient and client characteristics. Per prescription cost, per member per month (PMPM) total, plan and member costs and generic utilization rate were the targeted outcomes. RESULTS: The study group included 25 clients (106,718 lives) enrolled in 90-day retail program, and the control group included 25 propensity score matched clients (95,054 lives) not enrolled in the program. In the study group, the average total cost per prescription (normalized to 90-day supply) was significantly lower in 90-day retail than in mail service and 30-day retail ($165.9 vs. $170.65 vs. $185.9). The generic utilization rate in 90-day retail was higher than in mail service but lower than 30-day retail (38.36% vs. 37.38% vs. 39.75%). From the pre to post period, in study group, PMPM total, plan and member costs among eligible lives increased by 7% (from $29.54 to $31.60), 6.5% (from $22.29 to $23.73) and 7.3% (from $7.11 to $7.63). In the control group, PMPM total, plan and member increased by 10.1% (from $30.16 to $33.22), 10.4% (from $22.33 to $24.65) and 9.3% (from $7.72 to $8.43). It was estimated that this 90-day retail program had PMPM cost savings of $0.89, $0.79 and $0.10 for the total, plan and members. CONCLUSIONS: A 90-day retail program was found to have decreased total, health plan and member prescription drug costs.