Keratocystic odontogenic tumor (KCOT) is a benign cystic intraosseous tumor of odontogenic origin. An infection of a KCOT is not common because KCOT is a benign developmental neoplasm. Moreover, a severe deep neck space infection with compromised airway caused by infected KCOT is rare. This report presents a 60-year-old male patient with a severe deep neck space infection related to an infected KCOT due to cortical bone perforation and rupture of the exudate. Treatment of the deep neck space infection and KCOT are reported.