During October 21-26, 2007, wildfires consumed hundreds of thousands of acres and forced the evacuation of more than 300,000 persons in San Diego County, California. During large-scale emergencies, data are needed to assess health effects, plan response, and evaluate response adequacy. This report describes some of the health effects of the wildfires based on data from the CDC BioSense system, which receives emergency department (ED) patient chief complaint information and physician diagnosis codes from six hospitals in San Diego County. Analysis of these data indicated that ED visits for respiratory disease, especially those associated with dyspnea and asthma, increased during a 5-day fire period compared with the preceding 20 weekdays. For the six hospitals combined, visits for dyspnea increased from 48.6 to 72.6 per day, and visits with diagnoses of asthma increased from 21.7 to 40.4 per day. Local, state, and federal public health personnel should continue collaborative efforts to expand and