OBJECTIVES: The prevalence of dementia is growing considerately in the recent years. Little is known about how dementia affects care patterns after discharge for acute coronary syndromes. This study was designed to assess differences between care patterns for ACS patients with and without dementia. METHODS: We conducted a retrospective cohort study of 87298 patients hospitalized for ACS (1835 with dementia) from January 1, 2006 to December 31, 2007, based on a nationwide population-based data under national health insurance system. Primary outcomes were use of aspirin, beta-blocker, angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blocker (ARB), statin, and clopidogrel within 365 days after the first ACS event. Secondary outcomes were implementations of invasive procedures. Age-matched cohort at 1:2 ratio (N=5005) was identified to control for confounding variable age. Multivariate logistic regression was performed to examine the relationships between the diagnosis of dementia in ACS patients and their care patterns. RESULTS: ACS patients with dementia were less likely to receive aspirin (adjusted odds ratio (OR), 0.71; 95% CI, 0.64-0.78, p<0.001), beta-blocker (adjusted OR, 0.68; 95% CI, 0.61-0.75, p<0.001), ACEI or ARB (adjusted OR, 0.70; 95% CI, 0.64-0.78, p<0.001), statin (adjusted OR, 0.57; 95% CI, 0.50-0.64, p<0.001), and clopidogrel (adjusted OR, 0.84; 95% CI, 0.74-0.95, p=0.007) after the first ACS event compared with ACS patients without dementia. They were also less likely to underwent invasive procedures such as percutaneous transluminal coronary angioplasty (PTCA) (adjusted OR, 0.57; 95% CI, 0.51-0.64, p<0.001), coronary artery bypass graft (CABG) (adjusted OR, 0.31; 95% CI, 0.20-0.48, p<0.001), and revascularization (adjusted OR, 0.52; 95% CI, 0.47-0.59, p<0.001) during the first ACS event. Similar results were found in the age-matched cohort. CONCLUSIONS: The presence of dementia was associated with underutilization of evidence-based therapies in ACS patients. Influence of suboptimal treatments in ACS patients with dementia should be further evaluated.