Fifty-two cases of traumatic bone cysts in 50 patients were analysed clinically and radiologically. The obtained results were as follows; 1. Women showed a slightly higher incidence than did men (56% of patients) and the average age proved to be 18.6 years. 2. The majority of the cases were asymptomatic. being detected incidentally. and over the half of the cases occurred in the mandibular symphyseal region. 3. All cases were unilocular and the largest diameter of the lesions varied from 1 to 10㎝, mean 3㎝. 4. Some degree of marginal condensation was present in 28 cases and 23 cases presented pencil-sketch appearance. 5. Many anatomical cortical plates (especially, mandibular inferior cortex and lamina durae) consisted of the margin of the lesions partly. 6. Erosive change of the mandibular inferior cortex was caused by 12 cysts, but cortical expansion only by 3 cysts including 2 cases of buccal expansion. 7. The lesion enveloped the roots of the adjacent teeth in 27 cases and scalloping was present between roots in 17 cases. 8. Lamina dura of the teeth was destroyed by only 1 cyst, and in 1 case root resorption was noticed. But there was no divergence of the roots of teeth.