The aim of the study was to estimate the prevalence and localization of different types of gastrointestinal tumors in dogs and cats in relation to sex, age and breed of the animals. The study was performed on tissue specimens of gastric, intestinal, salivary gland, liver and pancreas obtained during surgery from dogs and cats submitted to the Division of Pathological Anatomy, Department of Clinical Sciences at the Agricultural University of Warsaw from 1996 to 2006. During this period 73 canine tumors and 14 feline tumors were recognized. In cats most tumors (92.8 % of the cases) were malignant, the most common were adenocarcinomas, rarely sarcomas and lymphomas. The tumors were localized mainly in the small intestine, liver and pancreas, large bowel tumors were not observed. The median age of affected cats was slightly more than 9 years, most of animals were male. Gastric and intestinal tumors in dogs were recorded in animals from 9 months to 14-years-of-age, more common in males. The tumors were most commonly derived from the large intestine, especially from the rectum; however the median age of dogs with lesions was lower than in animals in which neoplasms were present in other parts of the gastrointestinal tract. Of interest was the phenomenon that liver tumors, especially hemangiosarcoma, were often recognized in German shepherd dogs.