Although well defined pathologically, alveolar cell carcinoma can be difficult to diagnose because of its many clinical presentations. In a retrospective study of 45 cases, we reviewed the radiologic, pathologic, and clinical features of this neoplasm. Forty-one patients had a single peripheral mass that measured between 8 mm and 7 cm. Three patients had multiple nodules, and one had diffuse involvement of the right lung. Other prominent radiologic features included air bronchograms in eight cases, a "tail sign" in ten cases, and universal absence of calcifications. Pathologic examination showed an associated scar in 12 patients. There was a relatively high frequency (16%) of metachronous malignancies, including two osteosarcomas, three basal cell carcinomas, and one case each of chronic lymphocytic leukemia and thymoma. All but one of the associated tumors were diagnosed six months to two years before the diagnosis of alveolar cell carcinoma.