Thoracoscopic surgery is very useful in the mediastinal region, and it also expands the indications. The best indication for thoracoscopic surgery is benign mediastinal tumors. We performed thoracoscopic surgery for benign mediastinal tumor in 36 patients. These consisted of neurogenic tumor in 14 cases, teratoma in 2 cases, a mediastinal cyst in 19 cases, and Castleman's disease in 1 case. There were 3 cases which required an open thoracotomy for severe adhesion. However major complications were not seen. Myasthenia gravis not associated with thymoma is another good indication for thoracoscopic surgery. We have established techniques for thoracoscopic extended thymectomy combined with collar incision of the neck (TET) and performed TET in 18 cases of myasthnia gravis with satisfactory results. On the other hand, thoracoscopic surgery for thymoma is regarded as a necessary part of the operative procedure, and is regarded as indicated only for small, encapsulated, non-invasive thymoma.