We reviewed 4 cases of high‐grade transitional‐cell carcinoma (TCC) of the urinary tract with solitary pulmonary metastases that were studied by transthoracic needle aspiration biopsy cytology. There were two grade II and two grade III TCCs. The two grade II tumors yielded, in needle aspirates, syncytial tumor‐cell clusters showing ill‐defined, granular cytoplasm and slightly pleomorphic nuclei with inconspicuous nucleoli. In one case the tumor‐cell clusters showed a focal acinar arrangement, mimicking cells of an adenocarcinoma. In both cases the electron microscopy (EM) study of aspirated tumor cells revealed epithelial cells with well‐formed cell junctions, intracytoplasmic vesicles, apical short microvilli, and focal interdigitation of lateral cell membranes, suggesting a urothelial neoplasm. The two grade III TCCs yielded, in needle aspirates, pleomorphic malignant cells singly and in small clusters, showing well‐defined, granular cytoplasm and pleomorphic nuclei containing prominent nucleoli, suggesting a poorly differentiated adenocarcinoma or an anaplastic large‐cell carcinoma. By EM examination the aspirated tumor cells from one case revealed well‐formed cell junctions, intracytoplasmic vesicles, poorly formed microvilli, and focal interdigitation of lateral cell membranes, suggesting a urothelial differentiation. In the other case the tumor cells were pleomorphic cells with occasional cell junctions and no ultrastructural features as seen in the other 3 cases of TCC. The tumor cells from the two grade II TCCs showed strong immunopositive reaction with keratin 7 antibody and weakly positive reaction with carcinoembryonic antigen antibody (CEAA), while those of the two grade III TCCs displayed only a weak and focal immunopositive staining with keratin 7 antibody and strong reaction with CEAA. Diagn. Cytopathol. 1998;18:409–415. © 1998 Wiley‐Liss, Inc.