Mediastinal lymph node dissection for cancer of the left lung is more difficult than for cancer of the right lung because of the presence of aorta. Location and frequency of lymph node metastasis were examined for 231 left lung cancer patients who underwent pulmonary resection and mediastinal lymph node dissection, and survival rate of them was evaluated. Subaortic (# 5), paraaortic (#6), subcarinal (#7), tracheobronchial (#4) lymph nodes were the most frequently involved N 2 nodes. 5-year survival rate of the patients who had #4, #5, #6, #7, #8 or #9 lymph node metastasis was 20.7%. #4, #5, #6, #7, #8 and #9 should be dissected for the surgery of the left lung cancer.