HYPOTHESIS: Valuable lessons can be learned from the emergent evacuation of a large urban teaching hospital because of flooding. DESIGN: Case report. SETTING: Four hundred fifty-bed adult and 150-bed children's tertiary referral teaching hospital. CASE SUMMARY: Massive rainfall from tropical storm Allison caused extensive flooding. Emergency power came on at 1:40 AM. Complete power loss occurred at 3:30 AM. The decision to begin evacuation of patients was made at approximately 10:30 AM. All 575 patients were either discharged from the hospital (169 patients) or evacuated (406 patients) to 29 other facilities by both ambulance and helicopter by 3 PM the next day. Six deaths occurred, none of which could be attributed to the conditions created by the flooding. CONCLUSIONS: The lessons learned from this experience included the following: (1) flooding will occur in a flood plain; (2) electrical power outages are not necessarily temporary-begin evacuation; (3) appoint a triage officer from those available; (4) have a reliable in-house communication system not dependent on telephone lines or electricity; (5) have a reliable telephone system for contacting outside facilities; (6) have flashlights available on all units; (7) have battery-operated exit signs and stairway lights; (8) maximize use of volunteers when they are available and fresh; (9) maintain a paper record of all patient transfers; (10) coordinate loading of ambulances and helicopters for patient transfer; and (11) reassign staff as necessary to care for transferred patients. Emergent evacuation of a large, tertiary hospital requires extensive effort from both the hospital staff and the community.