A sudden and extensive power failure occurred at Karolinska University Hospital in Huddinge on Easter Saturday, 07 April 2007. The power failure lasted one hour and 22 minutes, but it took a longer time for activities to return to normal. It put many patients at great risk, particularly in the intensive care unit and other departments with critically ill patients. This report details the conditions and response at Karolinska University Hospital during the power failure and provides lessons learned for future events.