Adenocarcinomas of or in lung that clinically and pathologically mimic diffuse pleural mesotheliomas are rare. We reviewed selected clinical and pathologic features of 15 autopsy/surgical cases previously reported in the medical literature and of 15 additional cases from the files of the Armed Forces Institute of Pathology (AFIP). Ninety percent of the patients were men. The median age was 61 years. Sixty-three percent of the patients smoked, 17% of them had possible or definite occupational exposure to asbestos, and one patient had microscopically proven asbestosis. Most patients had chest pain, shortness of breath, or cough, and had unilateral pleural effusion in the chest x-ray. At thoracotomy or at autopsy, numerous nodules, plaques, or a continuous rind of tumor was present over the pleural surface. Microscopically, the tumors showed simplified glands, nests, cords, papillary, tubulopapillary or biphasic patterns of growth. The neoplasms contained mucin that stained with diastase-predigested periodic acid-Schiff (PAS), mucicarmine, and alcian blue (with or without hyaluronidase predigestion). All patients died with/of tumor, with a mean survival of 4.7 months for those reported in the medical literature and of 7 months for those in the AFIP files. These adenocarcinomas therefore mimic pleural mesothelioma not only in their clinical and gross and microscopic appearance, but also in their prognosis.