Vidio-assisted thoracic surgery[VATS] has recently evolved as an alternative to thoracotomy for several thoracic disorders,and the role of thoracoscopy has expanded with advances in surgical techniques and instruments. From May 1993 to May 1994, 13 patients with mediastinal mass underwent VATS for diagnosis and treatment at Gil General Hospital. There were four males and nine females, and their ages raged from 5 years to 66 years with average 38.8 years. Among 13 patients, 3 were operated for tissue diagnosis,9 for treatment,and 1 for diagnosis and treatment. Pathologic diagnoses were as follows; 5 benign neurogenic tumors, 2 thymoma, 2 sarcoidosis, 1 teratoma, 1 peripheral neuroepithelioma, 1 tbc lymphadenitis, and 1 pericardial cyst. The mean time of operation was 111.7 $pm$ 30.7 minutes[60-160], mean duration of chest tube drainage was 2.9 $pm$1.9days[1-9], mean hospital stay was 6.2 $pm$2.6 days[4-13]. There was no patient needed blood transfusion or conversion to open thoracotomy. Accurate diagnosis was possible in all patients operated for diagnosis and /or treatment.[4/4,100%] Two complications occurred in two patients: 1 transient Horner,s syndrome,1 anhydrosis of left arm. Compared with those of conventional thoracotomy done for mediastinal mass during previous 2 years[May 1991 - April 1993], operative results of VATS were better in all aspects. For mediastinal mass, we concluded that VATS can be done with less morbidity,less complication,less blood loss,shorter operation time and hospital stay,and not more expensive in cost than conventional thoracotomy. Noticeably, we think that VATS is the operation of choice for the diagnosis and palliation of malignant mediastinal mass.