OBJECTIVES To compare medication adherence for patients new to 90-day supply prescriptions under a new pharmacy benefit where pricing is equivalent, allowing members to choose either retail or mail pharmacy as their preferred distribution channel. METHODS Claims (n=168,381) submitted between Apri, 1, 2008 and December 31, 2008 for an employer after it began offering the same price on 90-day retail and mail maintenance prescriptions were used to calculate Medication Possession Ratio (MPR), Generic Dispensing Rate (GDR), Generic Substitution Rate (GSR), and Preferred Brand Dispensing (PBDR) for patients impacted by the benefit. GDR, GSR, and PBDR were calculated for all claims with a 90-day supply. MPR was calculated for all patients who were eligible 180 days before and after their first 90-day prescription between April 1 and June 30, 2008 for each maintenance class, using that first prescription and any within the subsequent 180 days. Overall metrics and those for select classes with sufficient sample size are presented. RESULTS The average MPR, across all classes, was 80% for retail dispensed prescriptions and 78% for mail. Among six high-volume classes, the average MPR was 82% at retail and 81% at mail, with MPRs for individual classes ranging from 75% (PPIs) to 89% (ACEs and Anticonvulsants) for retail-dispensed and 74% (SSRIs) to 85% (ACEs) for mail-dispensed. When comparing retail and mail dispensed prescriptions, GDR (57% vs. 56%), GSR (99% vs. 99%), and PBDR (86% vs. 86%) were nearly identical. CONCLUSIONS When out-of-pocket costs and days supply per prescription are identical, adherence rates and related formulary performance metrics for mail and retail-dispensed maintenance medications appear essentially similar in early results. These pilot results will need to be confirmed as more payers adopt this benefit design and longer follow-up periods improve adherence measurement precision.