Canine Transmissible Venereal Tumor (CTVT) is a benign reticuloendothelial (histiocytic) tumor of the dog that mainly affects the external genitalia. This tumor was found in male 2 years old mongrel dog. According the anamnestic data, there was no visible change of its general clinical status, except spontaneous bleeding with blood drops on the praeputium and the presence of blood in the urine. With clinical examination a multilobular mass on radix penis mucosa was found, which actually caused pseudohemorrhagia. The material for cytological diagnostic was taken with the imprint method and 4 cytological films were prepared and strained. The conclusion of the cytological diagnosis was CTVT. The tumor cause only local disturbances, and the differential diagnosis of the other "round cells tumors", histiocytomas, plasmacytomas, lymphoma, some melanomas and especially lymphosarcomas, which could be located on the external genitalia, had a big significance. Although some authors are mentioning spontaneous regression, however, because this is invasive tumor, a complete chirurgical excision was made.