When the TNM staging system of the American Joint Committee (AJC) for Cancer Staging and End-Results Reporting was applied to 3,912 patients seen during a 6 year period at the Mayo Clinic, 624 (16%) fulfilled the criteria for postsurgical pathological Stage I non-small cell bronchogenic carcinoma. Of these 624 patients, 129 were excluded from further survival analysis for various reasons. The remaining 495 consisted of two groups: 350 patients who were enrolled within 30 days into a prospective postoperative 4 monthly follow-up program and 145 patients who were enrolled later or were followed less frequently. Because no significant difference was noted in survival rates between these groups, data were pooled. Of the combined group of 495 patients, 84% survived lung cancer for 2 years and 69% of 5 years (actuarial estimation). The survival of patients classified T1 N0 M0 (91% alive at 2 years and 80% at 5 years) is so good that it seems unlikely that adjuvant therapy in this group could demonstrate improved survival. In addition to TNM classification, age at operation, sex, and extent of operation were important determinants of survival.