Adenocarcinoma has become the most common type of cancer of the lung. Its distinct natural history necessitates separation from the other cell types. Results from recent Veterans Administration Lung Group studies show that local-regional failure occurred in 59% of patients after irradiation for adenocarcinoma limited to the thorax. Data from 300 consecutive autopsies reveal that death was caused by intrathoracic complications of the tumor in 38%, and by metastases in 57% of patients. Adenocarcinoma has an intermediate risk of local and distant failure when compared to squamous and small-cell carcinoma. However, brain metastases are most frequent with adenocarcinoma. Preliminary results suggest that prophylactic brain irradiation decreases the frequency of brain metastases. Patients with adenocarcinoma are more likely than those with other cell types to have metastases only in the brain. Prophylactic brain irradiation may make the greatest contribution to improved survival in pateints with adenocarcinoma of the lung.