Pulmonary nodules morphologically indistinguishable from bronchioloalveolar carcinoma (BAC) were found in two adolescent cancer patients postchemotherapy. A solitary nodule was noted at thoracotomy for a single computerized tomography (CT) scan lesion in a 16-yr-old male, 6 yr after diagnosis of Ewing's sarcoma. A similar nodule was found in a 19-yr-old male coincident with resection of multiple lung metastases of a testicular germ cell tumor. Both lesions were discrete nodular masses (1 cm and 0.5 cm) consisting of atypical epithelial cells with a papillary and lepidic growth pattern and surrounded by histologically normal appearing lung. Immunohistochemistry of both cases was positive for laminoorganel (LO) antigen, which is found in normal type II pneumocytes, and one nodule showed carcinoembryonic antigen (CEA) staining. Quantitative DNA analysis in one case indicated aneuploidy. Thus the morphology, immunohistochemistry, and DNA content of these lesions suggest that they may represent early lung cancers despite the highly unusual clinical context. The extreme rarity of BAC in this age group makes this report significant in light of heightening concern about second malignancies in pediatric cancer patients and reports of chemically induced pulmonary adenomas in mice. It also underscores the importance of basing therapeutic decisions on a histologic diagnosis of lung nodules in cancer patients rather than assuming the presence of metastatic disease.