A 58-year-old woman was referred by her dentist to a maxillofacial surgeon because of a rapidly increasing facial swelling. The swelling developed after sodium hypochlorite irrigation during the endodontic treatment of tooth 25. A mechanical heart valve, a heart rhythm disorder, and antithrombotic therapy were complicating medical conditions. Treatment consisted of 12 mg dexamethason administered once intravenously, augmentin administered thrice daily intravenously, and oral analgetics. Damage following sodium hypochlorite irrigation during endodontic treatment is a rare disorder which is associated with a severe reaction in the surrounding tissue. Damage can be permanent.