SummaryAfter a review of the literature, the authors discuss the clinical, radiological and histological criteria of the alveolar carcinoma of the lung.The histogenesis of this disease is still a controversial issue.Most observers think the site of origin of the tumor is the pulmonary alveolas or the bronchis. Eck’s work suggests that alveolar carcinoma of the lung arises from an occultuous malignancy.Two typical cases of this disease entity are reported. A third case supports Eck’s view and stresses the hardnesses which may be encountered in the diagnosis of this tumor.