The purpose of this study was to investigate and to classify the patients of mandibular bone fracture who were hospitalized in the Kang-nam General Hospital. We observed clinically 57 patients from July 1983 to August 1988. The results obtained were as follows: 1. The ratio of male to female was about 6.1:1. 2. The highest age incidence was 3rd decade age group. 3. The most frequent etiologic factor was falling-down (36.8%). The next factors were fist-blow (31.6%), traffic accident (15.8%), sports (5.3%) and works (5.3%) in order. 4. The most frequent site of mandibular fractures was symphyseal area (23.1%), and mandibular angle (20.5%), condyle (19.2%), body (19.2%), alveolar bone (9.0%) and ramus (7.7%) were next in order.