During the evening hours of 3 May 1999, 58 tornadoes occurred in Oklahoma. One tornado reached F5 intensity and left a widespread path of death, injury, and destruction in and around the Oklahoma City metropolitan area. Other communities across the state were also affected. Data on persons who died or were injured were collected from medical examiner reports, hospital medical records, and follow-up questionnaires. In addition, community surveys were conducted in the damaged areas, and a random telephone survey of people in the Oklahoma City area was conducted. A total of 45 persons died, and 645 survivors were treated at a hospital for injuries/health conditions related to the tornadoes. Detailed analyses were conducted on the 40 deaths and 512 nonfatal injuries that resulted directly from the tornadoes. The average age of persons who died was significantly higher than that of injured survivors. Almost three-fourths (74%) of survivors were treated in an emergency department and released; 26% were hospitalized, with an average stay of 7 days. The most common kinds of injuries were soft-tissue injuries (cuts, bruises, and scrapes), fractures/dislocations, and brain injuries. The most common causes of injuries for survivors were being hit by flying/falling debris and being picked up or blown by the tornado. Probable causes of death included multiple injuries (50%), head injuries (23%), chest trauma (18%), and traumatic asphyxia (10%). The proportion of deaths among injured persons was higher in mobile homes, apartment buildings, and outdoors than in houses. The vast majority of persons received television warnings; few persons received warnings by weatherband radio. Survey data indicated that since the tornadoes there had been only a slight increase in the proportion of persons with a storm shelter on their home premises and in the proportion of persons who know the location of the nearest shelter. Effective preparedness plans should be developed in advance of situations with tornadic potential and implemented in a timely manner when warnings are issued. The accessibility and knowledge of the location of shelters also needs to be increased. Warning systems should be integrated and duplicative, and they should include traditional methods and new technology.