We report the cytologic feature.$ of eight fine-needle aspirations (FNA) and eight exfoliative specimens of collecting duct carcinoma (CDC) obtained from six patients. The four men and two women ranged in age from 27 to 69 years (mean = 45 yr) and all had advanced stage diseuse at presentation (one stage 111. five srage IV). Five of the six patients died of widespread disease, and one is alive and well (mean survival, 28 mo; range, 11-48 mo). The srnews of the FNA and exjoliative specimens were scantly to moderutely cellular. Tumor c e h showed moderate pleomorphism and were arranged primarily in cohesive groups that rarely had a papillary configuration. Nuclei had irregular nuclear contours, coarse chromatin. and one to three nucleoli. In the majority of c a w the cytoplasm was finely vacuolated, and occasionally there were large intracytoplasmic vacuole.. Intracytoplasmic mucin was demonstrated in two aspirates. Psammoma bodies were present in four of the seven juids. In rwo patients, the cytologic diagnosis WQS .supported by positive immunostaining jor high-molecular-weight kcratin and Ulex europaeus agglutinin I lectin. Leu M-1 was focallyposi1ive in one case and negative in the other. The cytologic j h u r e s of CDC were readily identiJied as malignant; however, they were not di.stincrive and overlapped with those of high-grade renal cell carcinoma with papillury features and transitional cell carcinoma.