The 2003 outbreak of severe acute respiratory syndrome (SARS) in Taiwan provided accelerated us to develop the most timely surveillance system1. Taipei, a metropolitan with many travelers annually, requires the earliest warningand immediate responses once novel agents would attack. Considering international exchanges of epidemiological information for travelers and possible cross-country spread of EID,we initiated an ED-SSS using clinical data involving checklist CoCo and ICD-9 plus IT internally installed mechanism integrated with epidemiological information to increase the sensitivity and timeliness to detect unusual outbreaks. Objective: To face challenges of emerging infectious diseases (EID) and bioterrorism and to prepare for international collaboration without language barriers, we established a timely hospital emergency department-based syndromic surveillance system (ED-SSS) using both triage predefined check-list chief complaints (CoCo) and International Classification of Diseases, 9th Revision (ICD-9) in Taipei. The aims of this study are: (1) to monitor the patterns and trends of Taiwanâs important infectious diseases using different syndrome groups [gastrointestinal (GI), respiratory, enteroviral infections, etc.]; (2) to integrate epidemiological attributes, syndrome groups and lab. findings for improving the sensitivity, specificity and timeliness of ED-SSS in detecting outbreaks; and (3) to compare the sensitivity, specificity, and kappa value of GI, respiratory, enteroviral and central nervous system (CNS) infections between CoCo and ICD-9.