Two hundred forty-four veterans, with a mean age of 62.4 years, mainly asymptomatic (pulmonary), were admitted generally for other disease or pension evaluation and underwent lobectomy (131), segmentectomy (107), or wedge resection (6) for T1 N0 M0 lung cancer between 1966 and 1988. Conservative resection was preferred during the past decade. The average lesion diameter was 2 cm. Thirty-day mortality was 2.9%, similar for the three procedures. Absolute 5-year survival, 51%, was 78% if only deaths from the initial lesion are considered; 19% died of comorbidity, and 8% died of second lung cancers. Routine preoperative computed tomographic staging and intraoperative sampling of even normal-sized hilar and mediastinal nodes, conducted after 1982, improved survival (p less than 0.006). Patients with lesions less than 2 cm in diameter (146) did better (p less than 0.04), and those with squamous tumors improved similarly (p less than 0.02). Lesions that communicated with a bronchus (88) were more malignant than those (156) that did not (p less than 0.02), because from that locus undifferentiated nonsquamous tumors metastasized widely. These results suggest that the T1 N0 M0 category is not uniform. Histology, size, and location in the lung are significant variables. Results of conservative resection were similar or better than those of lobectomy. The latter was used more in deep-seated lesions, however, when major intersegmental planes were transgressed, and before modern preoperative and intraoperative staging. The T1 N0 M0 category should include lesions 2 cm or less in diameter as a discrete entity.