We evaluated the effect of mediastinal lymph node metastasis on survival in 233 non-small cell lung cancer patients (N2 disease in 199 patients and N3 disease in 34 patients). Of the 199 patients with N2 disease, 144 underwent curative resection. The five-year survival rate of these 144 patients was 20.3 percent, which was significantly better than that of either the noncuratively resected N2 group or the N3 group. Nodal metastases in the curatively resected patients involved superior and inferior mediastinum irrespective of the location of the primary tumor. Patients with right-sided N2 lesions and metastases to the superior mediastinum had a worse survival than those with metastases to the inferior mediastinum. In contrast, patients with left-sided N2 lesions metastasizing to the inferior mediastinum had a significantly worse survival than those with lesions metastasizing to the superior mediastinum. Patients with single-level metastases had a significantly better survival rate than those with multilevel metastases. Subcarinal nodal involvement had an unfavorable effect in case of single-level metastasis, but did not affect the survival in cases of multilevel metastases. Our present study indicated that the survival of patients with N2 disease was affected by the operative radicality, by the number of levels of metastases, and also by the location of the nodal involvement. It seems appropriate that extensive mediastinal dissection should be performed irrespective of the location of the primary tumor.