A total of 178 patients with primary lung cancer who had undergone complete resection of the tumor in combination with complete mediastinal lymphadenectomy were reviewed at the Department of Thoracic and Cardiovascular Surgery of Yonsei Medical Center from January 1980 through July 1989. Materials; 1. There were 45 men and 33 women ranging of age from 25 to 78 years with a mean age of 55.4 years. 2. Histological types were squamous carcinoma in 115 cases [64.6%] adenocarcinoma in 42 cases [23.6 %], bronchioloalveolar carcinoma in 9 cases [5.1%], large cell carcinoma in 8 cases [4.5 %] and small cell carcinoma in 4 cases [2.2%] Results were summarized as follows: 1. The size of primary tumor was not directly proportional to the frequency of mediastinal lymph node metastasis. [P =0.0567] 2. The histologic types of the primary tumor did not related to the incidence of mediastinal lymph node metastasis. [P >0.19] 3. The chance of mediastinal lymph node metastasis in the case with lung cancer located in right middle lobe[31.8%, N=22] and left lower lobe [31.4%, N=32] were the highest and the lowest was the one located in right lower lobe, while over all incidence of mediastinal lymph node metastasis in this series was 25.4 % [N=55]. 4. The rate of mediastinal lymph node metastasis without evidence of regional and hilar lymph node metastasis was 13%. [N=23] The chance of mediastinal lymph node involvement without N1 lymph node metastasis was 16.3 % [N=17] in both upper lobes and 8.2 % [N=6] in both lower lobes. It was statistically significant that the tumors in the upper lobes had greater chance of the mediastinal lymph node metastasis without N1 than the tumors in the lower lobes. 5. In this series majority of the patients with lung cancer the mediastinal lymph node metastasis from the tumor in each pulmonary lobes usually occurs via ipsilateral tracheobronchial and paratracheal lymphatic pathway. Especially the lung cancer located in lower lobes can metastasize to subcarinal, paraesophageal and inferior pulmonary ligamental lymph node through the lymphatic pathway of inferior pulmonary ligament. It can be speculated that in some cases of this series otherwise mediastinal lymph node metastasis can also occur with direct invasion to the parietal pleura and to the mediastinal lymph node via direct subpleural lymphatic pathway .