Cytologic features of a case of inverted papilloma of the urinary bladder are described. A 33-year-old man presented with gross hematuria. Endoscopic examination revealed a pedunculated, non-papillary lesion measuring 15×10 mm near the left ureteral opening in the urinary bladder. Cytologic examination of the spontaneous urine exhibited small and intermediate-sized clusters of spindled-shaped cells with benign-looking oval nuclei with fine chromatin on a hemorrhagic background. Focal arrangement of tall columnar cells was observed. Histologically, the tumor was typical inverted papilloma. We should be aware of the cytologic features of this tumor in spontaneous urine samples.
