Data on the occurrence of cancers in dogs and cats from the Metropolitan Mesoregion of Belém are not available in the literature. This paper describes the occurrence of neoplasms in these species from 2005 to 2010. The canine cutaneous system was the most affected in this study (47%), followed by the mammary gland (39%), reproductive system (4%), oral cavity (4%), bones and joints (2%), ocular system (1.5%), digestive system (1.5%) and urinary tract (1%). In feline species, the mammary gland accounted for 87.8%, followed by the cutaneous system (6%), respiratory system (3%) and oral cavity (3%).