OBJECTIVES: Diabetes is an independent prognostic factor for increased risk for ischemic heart disease.  This study evaluates differences in health care costs and resource utilization for acute coronary syndrome (ACS) patients with and without diabetes mellitus (DM).  METHODS: :  A retrospective cohort study was conducted using a large US administrative claims database. Patients aged 18-65 years hospitalized with a primary diagnosis of ACS between January 1, 2005 and December 31, 2006 were identified and categorized into two groups: with DM and without DM.  Patients with complete insurance coverage and medication information 1-year prior and post the index hospitalization were included.  Annual health care costs (in 2008 US dollars) and resource utilization were compared for both groups (All p<.001 unless otherwise stated). RESULTS: Of 12,502 patients who met the study selection criteria, 3,040 (24%) were diabetic and 9,462 (76%) were non-diabetic.  Higher percent of diabetic patients had at least one all-cause rehospitalization event (49.0% vs 35.2%) or cardiovascular-related rehospitalization event (45.5% vs. 32.3%).  Mean length of stay (LOS) was longer for diabetic patients during the index hospitalization (4.3 days vs. 3.3 days), as well as during the rehospitalization event (all-cause: 4.6 days vs 3.3 days; cardiovascular-related: 4.6 days vs 3.2 days). In addition, patients with DM had more physician’s office visits (16.3 vs. 12.4), ER visits (0.8 vs. 0.5), and outpatient hospital visits (9.0 vs. 7.1) during the 12-month follow-up period.  Both cohorts had similar index ACS hospitalization costs ($32,026 vs. $29,082) but diabetic patients incurred higher rehospitalization costs (all-cause: $19,913 vs $10,947; cardiovascular-related: $18,256 vs $10,093), outpatient costs ($14,836 vs. $8,617) and pharmacy costs ($6,105 vs. $3,921).  One-year follow-up health care costs were significantly higher for patients with DM compared with those without DM ($40,853 vs. $23,485). CONCLUSIONS: The presence of DM significantly increases health care costs and resource utilization for ACS patient.