Purpose: This study was conducted to examine and compare the risk factors and clinical manifestations, and the treatment-seeking behaviors among patients <65 and ���65 years with first-time acute coronary syndrome (ACS). Methods: A total of 288 patients diagnosed with acute myocardial infarction (n=267) and unstable angina (n=21) were individually interviewed following percutaneous coronary intervention from November, 2007 to December, 2008. From the qualitative interview data, significant variables were coded and analyzed using SPSS version 15.0. Results: Younger patients (n=142) were more likely to have current smoking (56.7%), bad eating habit (45.8%), obesity (39.8%), emotional stress (26.8%) and family history (31.7%), and to complain chest pain, left shoulder and arm pain, perspiration, and nausea compared to older patients. Older patients (n=146) were more likely to have hypertension (65.1%) and diabetes (43.8%), and to complain atypical symptoms including syncope and dyspnea. Median pre-hospital delays for younger and older patients were 5짹57.6 and 12짹56.2 hours, respectively, and different meaningful interpretations to their symptoms were found. Logistic regression analyses showed that after adjustment for gender and education, progressive onset of symptom and no attribution as cardiac problem significantly predicted pre-hospital delay >3 hours in both patients. No chest pain as a chief complaint predicted the delay for younger patients and low perceived health status for older patients. Conclusions: Health care providers should concern more on lifestyle modification such as smoking cessation and increasing physical activity for younger adults. Also, they should alert on the management of hypertension and diabetes for older adults. It is important to educate the public on early symptoms and actions needed based on differed coping behaviors of younger and older adults.