An in-depth retrospective statistical analysis was performed on 150 consecutive cases of adenocarcinoma of the lung. One-hundred and twenty-eight patients (85%) underwent pulmonary resection; 15 (10%) had an explorative thoracotomy and 7 (5%) were considered inoperable. At the time of operation, 72 patients were classified as Stage I, 18 as Stage II and 50 as Stage III. Factors analyzed included age, sex, surgical treatment, staging, immunologic monitoring and survival. When compared with other histotypes of our series a statistically significant difference was found in the male: female ratio (p less than 0.05), surgical resectability (p less than 0.05), frequency of Stage I, and immunologic status evaluated by studies of delayed hypersensitivity skin tests, lymphocyte blastogenesis, antibody dependent cellular cytotoxicity (ADCC), blocking serum factors and intrastromal peritumoral lymphocyte infiltration. There were no significant differences due to age, cigarette smoking, mediastinal lymph node involvement, except for small oat-cell carcinoma or previous pulmonary diseases. In all stages, the five-year survival rate was lower for patients affected with adenocarcinoma than for those affected with other histological types, except small oat-cell carcinoma.