After Hurricane Katrina struck the U.S. Gulf Coast on August 29, 2005, approximately 200,000 evacuees were sent to shelters in 18 states. On September 3, 2005, Colorado was asked to assist in sheltering some of the evacuees; the next day the first evacuees were airlifted into the Denver area, where they were housed at the former Lowry Air Force Base. During the next 4 weeks, 3,600 evacuees registered at Lowry, with an average of 400 persons in residence per day. Other persons self-evacuated to other parts of the state, including approximately 2,000 who went to Colorado Springs. In all, an estimated 6,000 evacuees were living throughout Colorado in the weeks after Hurricane Katrina. As a result of the influx of evacuees, the Colorado Department of Public Health and Environment (CDPHE) and the Tri-County Health Department (TCHD) established surveillance systems to provide early detection of outbreaks and determine the scope of medical conditions of evacuees. A rapid needs assessment also was conducted at the local level to assess acute medical and other needs of evacuees. Results indicated that many evacuees had chronic conditions and approximately half planned to remain in the area, suggesting a long-term need for increased health-related and other services. In addition, the most common acute symptoms were related to altitude sickness, requiring education of incoming Gulf Coast evacuees regarding the effects of the mile-high altitude in Denver.