The article presents the results of a study on the primary incidence of malignant tumors in dogs and cats in Moscow over the period from January 1, 2023, to July 1, 2024. The study was conducted on the basis of the Department of Diseases of Small Domestic, Laboratory and Exotic Animals and the Research Laboratory of Oncology, Ophthalmology and Animal Biochemistry of the Russian Biotechnological University “ROSBIOTECH”. The study included 208 cats and 325 dogs with primary, spontaneous malignant tumors of various origins. To confirm the diagnosis, a comprehensive approach was used, including clinical examination, hematological tests, and special diagnostic techniques such as ultrasonography, radiography, computed tomography (CT), and magnetic resonance imaging (MRI). Verification of the tumor process was based on cytological and histological methods.The purpose of this work is to analyze the structure of the incidence of small domestic animals with malignant tumors. As a result, we identified the most common types of tumors in cats and dogs. In cats, breast carcinoma was the most common type (44.23%), followed by lymphoma (18.27%), sarcomas (13.46%) and carcinomas (13.94%), as well as squamous cell carcinoma (6.25%). In dogs, breast carcinoma also accounted for the majority of cases (37.23%), along with sarcomas (23.38%), mastocytomas (16.31%), and carcinomas (14.15%).