The clinical presentation of Ludwig's angina consists in a severe expanding cellulitis causing swelling of the floor of the mouth, tongue and submandibular region, thus resulting in a possible obstruction of the airway and in a rapid progress in deep neck soft tissue infection and mediastinitis with potentially fatal consequences. Frequently, submandibular cellulitis develops from an acute infection spreading from the lower molar teeth. Mandibular fractures, traumatic laceration of the floor of the mouth, and peritonsillar abscesses are other concomitant clinical features. A case of Ludwig's angina associated with a large erupted odontoma and with a deeply impacted third molar displaced to the border of the mandible is described. The patient was affected by enlargement of submandibular space, marked face swelling causing an evident face deformity, tenderness and redness of the neck and limited movement of the neck and mouth. In the past, Ludwig's angina was frequently fatal, however aggressive surgical and medical therapy have significantly reduced the mortality rate. The reported case can be considered as important, not only because of the rarity of the odontoma eruption in the oral cavity, but mainly for the extent of the clinical manifestation of a lesion usually described in literature as asymptomatic.