Purpose: The aim of this study was to examine characteristics of health-related victims identified through the Surveillance System of Heat-related Illness (SSHI) based on emergency department (ED) visits. Methods: Between July 1 and September 3 of 2011, 443 heat-related patients were reported by 396 of the 461 EDs participating in the SSHI. Heat-related illness included heat (sun) stroke, heat cramp, heat syncope, and heat exhaustion. A hot day was defined as a day above 30?C of daily maximum temperature in locations of provincial and metropolitan government offices. We used chi square test for identification of risk factors associated with Heat-related illness in the workplace and heat-related illness heat (sun) stroke. Results: Heatwave, defined as lasting three or more hot days, occurred three times during this period. The daily average number of heat-related patients reported during the heatwave period was 15.7 per day, more than four times the usual rate. The daily maximum temperature showed positive correlation with occurrence of heat-related illness. Heat exhaustion was the most frequent cause (46.0%), with approximately 70% of all cases occurring between noon and 6 p.m. The number of people suffering from heat-related illness while outdoors was three times greater than that of those who experienced it indoors. Work-related occurrence comprised 56.7% of all cases. All six deaths occurred during the heatwave period and were work-related. Conclusion: Working conditions, outdoor activities, and old age may be associated with health-related illnesses. A surveillance system that monitors emergency room visits may be useful in assessment of adverse health effects of summer heatwaves.