OBJECTIVES To determine the effect of a formulary change in the statin drug class on health outcomes and disease-specific health care costs. METHODS A retrospective cohort design was implemented using pharmacy and medical claims data from a large national employer group. Patients (n=330)with one or more claims for atorvastatin or another statin during the six months prior to a formulary change on January 1, 2006 were identified and evaluated. The formulary change was implemented for all patients however, only those patients taking atorvastatin were affected. Cardiac-related medical events (tests, doctor visits, outpatient facility visits, and acute cardiovascular events) and disease-specific costs during the year following the formulary change were measured. The impact of formulary change on cardiac-related medical events and disease-specific costs were evaluated using multivariate analysis controlling for gender, age, comorbidity status, and drug indication (primary vs. secondary prevention). RESULTS Of the 330 patients, 180 (55%) used atorvastatin prior to the formulary change. After the implementation of the formulary change, 146 (81%) of patients switched to a preferred statin drug, 19 (10%) discontinued statin therapy, and 16 (9%) continued taking atorvastatin as a non-preferred drug. There were no significant differences in the proportions of patients with cardiac tests (p=0.70), doctor's visits (p=0.64), outpatient facility visits (p=0.52), or acute cardiovascular events (p=0.13) in the year after the formulary change between patients with pre-formulary change claims for atorvastatin or another statin. There were no statistically significant differences in health care costs among patients with pre-formulary change claims for atorvastatin or another statin after adjustment for covariates (OR = 0.89, 95% CI: 0.41-1.92). CONCLUSIONS Changing the formulary status of atorvastatin does not appear to adversely affect the total medical costs or utilization of cardiac-related health care services.