Between 1974 and 1988, 115 patients admitted to our surgical unit underwent resection of nonsmall-cell lung cancer in the presence of mediastinal lymph node involvement (N2 disease). The overall 5 year survival rate was 18%, and the rates in patients with curative and noncurative operation were 26% and 9%, respectively (P less than 0.05). Based on the morphological evidence of N2 disease, the patients were placed in three groups: those with microscopic metastasis, moderate metastasis, and gross metastasis, the incidences being 29%, 28%, and 43%, respectively. The survival rates were 41%, 6%, and 16%, respectively. The difference among microscopic vs. moderate and microscopic vs. gross metastasis was statistically significant (P less than 0.01). Survival rates in patients with intranodal and extranodal invasion, as seen in the histologic examinations, were 34% and 11%, respectively (P less than 0.01). The incidence of gross metastasis and/or extranodal invasion was higher in those who underwent noncurative operation. Postoperatively adjuvant irradiation was not effective in prolonging the survival in patients with curative operation, but the local residual disease was controlled. Therefore, our working criteria are, if N2 lung cancer is present, a complete resection of the primary tumor and the mediastinal lymph nodes should be done. Patients with microscopic metastasis and intranodal invasion can expect a fairly long survival.