A prospective study of prognosis factors for operated non-small-cell bronchogenic cancer was conducted to assess those proposed by the T.N.M. classification. From April 1984 to December 1993, 918 patients aged 32 to 83 years underwent surgery: 389 stage I; 367 stage II; 367 stage IIIa; and 25 stage IIIb. Macroscopic exeresis was satisfactory in all patients and node dissection of the mediastinum was performed. Post-operative mortality was 4%. Overall actuarial survival at 5 years was 43.9%, stage I 59.5%; stage II 53.8%; stage IIIa 25.1%; stage IIIb 29.3%. Tumor size, presence of visceral pleural invasion, and presence of local invasion (T3 and T4) worsened prognosis (concerning T). The prognosis value of N was the determining element: survival at 5 years, 56.3% for N0; 47.5% for N1 and 20% for N2. When metastases invaded two node chains in combinaison with T3, prognosis was poor. These cancers were stage IV.