The incidence of deep neck infections continually declined since the advent of antibiotics. In the past times, infections of the pharynx and tonsil were the most frequent causes of deep infections, but recently dental infections become more important causes. Authors reviewed 24 patients with deep neck infections in special reference to the differences between deep neck infections caused by odontogenic (OD) problems and those caused by non-odontogenic (NOD) problems, and obtained following results. The most common single cause was odontogenic problem, followed by unknown cause. Trismus and dyspnea were more prevalent symptoms in OD group. The most common deep neck space involved was submandibular space in OD group, visceral space in NOD group. The case which involved more than one space was more prevalent in OD group. The presence of gas was more prevalent in OD group. The surgical treatment was required in all OD group, but some NOD group were treated by only conservative treatment. So OD group had more severe clinical courses and required more aggressive treatment than NOD group.