Little is known about the risks, hazards, and health outcomes for health care personnel and volunteers working in disaster relief. We sought to characterize risks and outcomes in volunteers deployed to provide relief for victims of Hurricane Katrina. We performed a longitudinal e-mail survey that assessed preventive measures taken before and during deployment, exposures to hazards while deployed, and health outcomes at 1, 3, and 6 months postdeployment. Overall response rate was 36.1 per cent and one-third of those who responded did so for all three surveys. Exposures to different types of hazards changed over time with exposures to contaminated water being common. Despite predeployment and on-site education, use of preventive measures such as vaccination, appropriate clothing, hydration, sunscreen, and insect repellant was variable. Few injuries were sustained. Insect bites were common despite the use of insect repellants. Skin lesions, diarrhea, and other gastrointestinal complaints occurred most commonly early on during or after deployment. Psychological complaints were common at 3 and 6 months. In conclusion, identification of at risk volunteer cohorts with longitudinal surveillance is critical for future disaster planning to provide training for volunteers and workers and to allow for deployment of appropriate resources pre, during, and postdeployment.