Since 1979, 109 patients underwent bilateral mediastinal lymph node dissection through a median sternotomy as a routine procedure in the treatment of left lung cancer, because of the high possibility of contralateral mediastinal node involvement in cases of left lung cancer. The five-year survival rates of the initial 50 patients who underwent this operation from Oct. 1979 till Mar. 1988 were 76.5% in N0 (n = 17), 69.2% in N1 (n = 13), 50.0% in N2 (n = 10) and 20.0% in N3 (n = 10). The five-year survival rate of 7 patients with pT1-2 N2M0 disease was 71.4%. This survival rate was only slightly different from that of the pT1-2N0-1M0 group. From May 1985 till April 1993, 20 patients who had the cervical or the highest mediastinal lymph node involvement underwent cervical and bilateral mediastinal lymph node dissection through a cervical collar incision and median sternotomy. Two patients with the scalene node involvement (one each of right and left lung cancer) are surviving for five years or more after surgery. Extended ipsilateral mediastinal lymph node dissection (R2b) has been adopted as a routine procedure in the treatment of right lung cancer in our institute since 1990. The survival rate at forty months in 15 patients with N2 disease who underwent R2b operation was 51%. In 3 of these fifteen patients the anterior mediastinal lymph node metastases were revealed by post-operative pathological investigation.(ABSTRACT TRUNCATED AT 250 WORDS)