Анотация: An extragenital canine transmissible venereal tumour was described pathomorphologically and immunohistochemically in the nasal sinus of a 7-year-old female German Shepherd dog. The tumour removed from the nasal sinus weighed 45 g and was multilobullary, firm in consistency, with grayish-white colour. Histopathologically, ovoid- or round-shaped neoplastic cells with prominent, clear, large, round to ovoid hyperchromatic nuclei were seen. In general the cells were with a less dense distinct cytoplasm, solid or in cords. Immunohistochemically, positive reactions in tumour cells were detected by p53 protein, vimentin and alpha1 chymotrypsin antibodies