To evaluate mediastinal lymph node dissection, the Lung Cancer Study Group of 21national sanatoria analyzed the postoperative mortality, survival and site o recurrence in patients consisting of two groups: there with a simple procedure involving only searching for hilar and mediastinal lymph nodes for biopsy (R1) and the other, a radical procedure with mediastinal lymph node dissection (R2). From 1979 to 1981, 606 patients were underwent potentially curative resection for Stage I or II non-small cell carcinomas of the lung. The mortality rates of the radical and simple procedures were similar. The 4-year survival rate was belles in the radical procedure, significantly (p<0.01). Local recurrence was more often seen in the R1 group than in the R2 group of patients, and the difference was significant. In the light of the data presented, attitudes fowords mediastinal dissection should be reevaluated for the treatment of the lung cancer.