BACKGROUND: Hurricane Katrina necessitated the evacuation of over 200,000 New Orleans residents into Houston in the days after landfall. The already stressed emergency departments (EDs) were faced with a potential influx of patients suffering injuries and conditions exacerbated by the hurricane and resulting devastation. OBJECTIVE: To examine the effect of Katrina evacuees on Houston EDs after the hurricane. DESIGN: Data from visits to 25 Houston EDs in 2005 (n Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 875,750) were analyzed to evaluate the impact of visits by Katrina evacuees (n Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 8427). MEASURES: Descriptive counts of ED visits by individuals with a FEMA designated disaster area zip code due to Katrina. RESULTS: In September, immediately after Katrina, Houston-area EDs reported the lowest monthly total visits in 2005 despite treating 4518 evacuees that month. On aggregate, the increase in visits by evacuees did not overwhelm area EDs, as they coincided with a decrease in ED utilization by nonevacuees and over 20,000 evacuees were seen at medical clinics in the large shelters. The highest number of evacuee visits to an individual ED was 86, on September 1. The peak day of visits, totaling 364, occurred on September 3. The ED that bore 15% of total visits saw no more than 19 evacuees daily. Evacuee and nonevacuee visits dropped dramatically when hurricane Rita threatened Houston. CONCLUSIONS: Houston EDs experienced an increase in visits by Katrina evacuees in the hurricane's aftermath. However, the initial surge of visits was modest and corresponded with decreases in visits by nonevacuees and medical care provided in large shelters.