Potentially lethal consequences can quickly occur once the mediastinum is subjected to the ravages of an anaerobic infection. Mediastinitis from odontogenic or deep cervical infections is extremely rare in the era of antibiotic drugs. We have recently encountered five such cases, with a rapid spread of the inflammatory process into the mediastinum resulting in a number of local and systemic complications. All were caused by anaerobic bacteria. Awareness of such complications and early roentgenographic diagnosis lead to prompt surgical drainage, proper antibiotic therapy, and survival after a stormy clinical course. The anatomic pathways between the various fascial planes of the neck and mediastinum will be described.