Under the category of benign adenomas of the lung, the current World Health Organization classification of Tumors recognizes mucous gland adenoma, mucinous cystadenoma, pleomorphic adenoma, alveolar adenoma, and papillary adenoma. Here we discuss only alveolar adenomas. Alveolar adenomas are rare, benign usually solitary, peripherally located proliferations made of a network of cystic spaces lined by simple cuboidal epithelium, resembling type II pneumocytes. The epithelium in some of these adenomas may become so flattened that it may look like endothelium, closely mimicking vascular proliferations. In these instances, immunostaining for vascular markers such as CD31 or CD34 and epithelial markers such as pancytokeratin or epithelial membrane antigen can help to make the distinction. In one series of six patients with alveolar adenoma, the mean age was 59 years and patients were all asymptomatic. In chest radiographs and CT studies, alveolar adenomas may appear as non-calcified coin lesions in the subpleural zones of the lung. Due to their peripheral location, little is known in terms of their endoscopic appearance or cyotpathologic features.