OBJECTIVES: Little information exists regarding costs of acute coronary syndrome (ACS) in the setting of an integrated health care program. The purpose of this study was to estimate total costs of new onset ACS from index hospitalization through one year. METHODS: This descriptive analysis consisted of Kaiser Permanente Medical Care Program patients age > 40 years and hospitalized with an ACS diagnosis during January 1, 1999 to December 31, 2000. Patients were required to be without ACS diagnoses in the six months before the index event. Follow-up continued for one year. A gender and age matched control group was created at a 5:1 ratio (control:ACS patient). Costs expressed are those incurred by the health plan. RESULTS: In total, 14,852 patients met inclusion criteria (7,919 myocardial infarction [MI], 6,933 unstable angina [UA]). Mean age was 67.2 years, and 63.9% were male. During the first year after the index event, rehospitalization occurred in 13.5% of patients for MI, 17.2% for UA, and 38.5% for all coronary heart disease. Index hospitalization costs were $6802 for ACS cases. Total costs (mean ± SD) from discharge through one year were $20,743±30,159 ($12,163 median) for ACS cases and $3,679 ±12,495 ($1,089 median) for controls. Males and females with ACS had similar mean costs ($20,894±31,179 vs. $20,475±28,262) while ACS cases age >65 ($21,354±27,904) had somewhat higher mean costs than those age <65 years ($19,862±33,126). Percent of total costs by type of resource used (clinic, hospital, and pharmacy, respectively) for ACS cases was: 19.4%, 70.3%, 6.2%; for controls: 38.4%, 43.5%, 13.0%. CONCLUSIONS: Hospitalization for ACS was associated with substantial costs for the index event as well as large additional costs through one year. The largest contributor of costs was hospital-related (70%). Rehospitalization also occurred frequently in ACS patients.