Factors affecting stage I epidermoid cancer of the lung were studied in a series of 29 patients treated only by surgery and followed up for ten years. A set of 13 variables with a possible influence on prognosis were investigated. The application of the Cox Univariate Analysis to the different variables showed the grade of cell differentiation and the mitotic index to be predictors. In the Cox Multivariate Analysis, the proportional regression equation revealed two independently significant variables (p < 0.01), which were the Mitotic Index and Nuclear Area. Grouping patients on the basis of the prognostic variables indicated allows a better prediction for survival to be made for this series of patients.