Purpose: To outline the lessons taught by Hurricane Katrina during the evacuation, cleanup, and rebuilding phases of a radiation oncology center in the hope that others may benefit from our experiences in formulating their own disaster and recovery plans. Method and Materials: Hurricane Katrina flooded 80% of the city of New Orleans including our radiation oncology department. Procedures developed prior to the storm to ensure communication among staff and patients, to minimize loss of patient and physics/dosimetry data, and to expedite recovery were put to the test. Results: Several unexpected situations arose during the evacuation, cleanup, and rebuilding phases: cell phone service was interrupted for several weeks and hospital email servers were down for months; most surviving patient and physics data were found to be remote electronic backups; securing of radioisotope sources was hampered by the loss of safe keys and the lack of functioning elevators; many patients were unable to relate their diagnoses and treatment histories to their new care providers; further equipment and data loss occurred after the primary catastrophe; vender maintenance agreements greatly decreased replacement costs of replacement computer systems; the pace of rebuilding was slowed by external influences; and extra training was required after the long closure. Conclusion: Even the most careful planning cannot account for the unexpected. But because of careful planning, both pre‐ and post‐Katrina, our flooded radiation oncology department reopened in November 2006 and remains the only flooded radiation facility to do so 18+ months after Katrina. Most of the unforeseen situations encountered can now be planned for in future disaster and recovery plans. © 2007, American Association of Physicists in Medicine. All rights reserved.