Purpose : The purpose of this study was to determine the prevalence, radiographic appearance, and characteristics of patients with zygomatic air cell defect (ZACD), and to give recommendations concerning radiographic evaluation and surgery. Materials and Methods: Routine panoramic radiographs of 1,400 patients admitted to the Kyungpook National University Hospital Dental Clinic, were retrospectively examined for the clinical and radiographic features of ZACD. Results: ZACD was found in 31 cases, representing a prevalence of 2.2%. Patients with ZACD had a mean age of 27.5 years and a range of 9-52 years. Most ZACD cases were in their thirties. ZACD showed a strong male prediliction, 22 of the 31 subjects were males and 9 were females. Twenty-four cases of ZACD (77.4%) were unilateral, with the half occurring on the right side. In seven cases (22.6%), ZACD was bilateral. Twenty-six (68.4%) of the defects were of unilocular, while twelve (31.6%) of the defects were multilocular. Conclusion: Knowledge of ZACD may be helpful in interpreting images, including panoramic radiographs, in planning surgical treatment of the TMJ and in understanding the spread of pathological processes into the joint.