A review of 50 patients with primary mediastinal tumors or cysts has been done to evaluate clinical and pathological behavior of this heterogeneous group of tumors proved by either excision or biopsy from January 1980 to August 1989 at the cardiovascular department of surgery in Kyungpook National University Hospital. There were 30 males and 20 females in this series. The ages of patients ranged from 4 months to 64 years. The mean age of subjects was 30.4 years. Neurogenic tumors [14 cases, 28%] and teratoma [14 cases, 28%] were most frequently encountered and followed by thymoma [10 cases, 20%] and benign cysts [4 cases, 8%]. The anatomic location of the primary mediastinal tumors or cysts was classified as anterior mediastinum and middle or visceral mediastinum and paravertebral or costovertebral mediastinum on the basis of the Shields’ proposition. In 32 patients[64%], the tumors or cysts were located in anterior mediastinum and in 13 patients[26%], the tumors or cysts were located in paravertebral or costovertebral mediastinum. And the rest 5 patients[10%] had middle or visceral mediastinal tumors or cysts. One of the characteristic features of primary mediastinal tumors or cysts is that some mediastinal tumors or cysts have their own preferred location in the mediastinum. In our series, all of the 14 patients with teratoma and 10 patients with thymoma had the anterior mediastinal location, while 13 of the 14 patients with neurogenic tumors had the paravertebral mediastinal location. 14 patients[28%] were asymptomatic and they all were discovered via so-called “Routine” chest x-ray examination. 39 of 50 patients[78%] were benign. 11 patients[22%] were malignant and they were all symptomatic. 40 patients[80%] were treated with complete resection. 5 patients[10%] were treated with partial resection : 2 of malignant thymoma, 3 of lipoma, neuroblastoma, primary squamous cell carcinoma. The rest 5 patients[10%] were only biopsied: 2 of undetermined malignancy and 3 of hemangioma, lymphoma, primary squamous cell carcinoma. 4 of the 10 patients were treated with combination of irradiation and chemotherapy. Postoperative complications were as followings: Horner’s syndrome [4cases, ado], respiratory failure [3 cases, 6%], pleural effusion[3 cases, 6%], Wound infection[2 cases, 4%] and bleeding, pneumothorax, empyema. There were 5 postoperative deaths [10%]. One patient with neuroblastoma died from intraoperative massive bleeding, 3 patients died early postoperatively from respiratory failure with undetermined malignancy died late postoperatively from congestive heart failure due to direct invasion of the tumor to the heart.