The gross pathological, microscopic, and clinical features of 173 Stage I and Stage II primary nonsmall cell carcinomas resected for cure by segmental resection, lobectomy, or pneumonectomy at the Johns Hopkins Hospital were analyzed to determine which provided useful independent prognostic information. The tumors studied included 79 squamous carcinomas (56%); 74 adenocarcinomas (44%), including 15 undifferentiated tumors which contained intracellular mucin; 18 large-cell undifferentiated carcinomas (10%); one giant cell carcinoma (less than 1%); and one adenosquamous carcinoma (less than 1%). Clinical features evaluated for each case included age, sex, race, and history of previous or subsequent malignancy; and pathologic features evaluated included tumor size, lymph node metastases, tumor location, cellular anaplasia, desmoplastic response, inflammatory response, preexisting scar, tumor necrosis, and degree of tumor differentiation. Multivariate analysis using the Cox life table regression model indicated that five features had a significant (p less than 0.05) independent association with subsequent death due to the tumor, and that the final set was highly significant (p = 0.001). These features were the following: large-cell undifferentiated histology, lymph node metastases expressed as N classification, tumor size expressed as T classification, tumor giant cells in any histologic type, and absent or minimal plasma cell infiltration. No additional prognostic information was obtained from any of the other features analyzed.