Atrial fibrillation (AF), the most common persistent arrhythmia, increases the risk of stroke manifolds. This risk is further enhanced in the presence of underlying cardiovascular diseases (CVD). Yet, the health care costs and utilization associated with this condition have not been well studied. OBJECTIVE: To compare the resource utilization and costs among patients with and without AF in an employer-based privately insured population with underlying CVD. METHODS: Retrospective claims data from a large group of self-insured employers were used. Patients continuously enrolled from 1/1/96 to 12/31/97 with at least one ICD-9 code of ischemic heart disease or heart failure in 1996 were included. From this cohort all patients with AF (ICD-9 427.31) were identified and two non-AF controls were randomly selected for each case. Resource use and charges were compared using univariate tests. Logistic and log-linear regression techniques were also used for risk-adjustment. RESULTS: 3.3% of AF-patients (n=831) and 2.5% of non-AF patients (n=1662) had a cerebrovascular event in 1997. One-year median resource use in the AF and non-AF group was as follows: hospital days: 7.0 vs 6.0; outpatient visits: 8.0 vs 6.0; home health visits: 6.0 vs. 5.0; ER visits: 1.0 vs. 1.0, nursing home days: 7.5 vs 6.0. The median annual total charges per AF patient and non-AF patient were $22,213 and $17,472, respectively. On controlling for age, gender, Charlson Comorbidity Index, type of CVD, and prior year's hospital use, the two groups only differed significantly in number of outpatient visits. No differences in costs existed. CONCLUSIONS: AF patient had a higher utilization of outpatient visits as compared to non-AF patients. It is possible that presence of severe underlying CVD in both groups overwhelms the differences in the costs attributable only to AF. Further examination of the pharmacy data will help reveal any differences in drug utilization and costs due to AF.