OBJECTIVE:: To determine the impact of adherence to antihyperlipidemic drug therapy on patients' total pharmacy and medical costs, from the payer's perspective. METHODS:: Retrospective database analysis of Maryland Medicaid medical and pharmacy claims for the period January 1, 2001 - December 31, 2003. Inclusion criteria: Continuously enrolled patients older than 18 years who had at least one prescription claim for any of the statins. Exclusion criteria (to obtain incident cohort): Patients who had at least a claim before July 1st, 2002. Non-adherence was defined as a failure to refill a prescription claim. Generalized linear models with a logarithmic link function were used to determine the impact of adherence to statins on medical costs, after adjusting for age, gender, race and comorbidities by constructing a Charlson Comorbidity Index. RESULTS: Total of 2746 patients, 34% male, 44% African-Americans, and 65% older than 63. Patients who adhere to their antihyperlipidemic pharmacotherapy incur 26.08% (p<0.0001; CI -0.41, -0.19) and 33.25% (p=0.0002; CI -0.62, -0.19) lower total costs (pharmacy and medical) and medical costs respectively than those who do not. Those between the age of 40 and 63 and those who are African-American incur 19.22% (p<0.0001; CI -0.31, 0.11) and 14.05% (p=0.002; CI –0.25,-0.05) lower total costs than those who are older than 63 and those who are Caucasian respectively. A unit increase in the comorbidity index leads to a 10.13% (p<0.0001; CI 0.07, 0.12) increase in total costs. CONCLUSIONS: On average, adherence to antihyperlipidemic pharmacotherapy results in lower total costs. More awareness given to adherence patterns on statins could lower the payers' total medical costs.