A retrospective study of 34 patients (33 male and one female) was conducted to evaluate a potential correlation between patient survival, propensity to metastasize and specific subtypes of pulmonary adenocarcinomas as determined by ultrastructural examination. Previous electron microscopic studies of pulmonary adenocarcinomas have demonstrated proliferations of three types of cells: mucus, Clara, and alveolar cells. Specific ultrastructural markers of these cell types were assessed in the 34 cases. All cases in this study had a light microscopic diagnosis of adenocarcinoma originating in the pulmonary parenchyma and a follow-up of at least one year. Features such as patient survival time, extent of metastatic involvement, response to therapy, and overall tumor behavior were compared in reference to the cell of origin, in an effort to try to elucidate if such ultrastructural subclassification lent itself to any clinical correlations. Light microscopic growth patterns and special stains were not found to distinguish these neoplasms histogenetically, emphasizing the important role of electron microscopy for an accurate classification.