The study aimed to determine the frequency of neoplasmas that were histopathologically diagnosed at the Pathology Laboratory of School of Veterinary Medicine, San Marcos University in the period 1996-2007. The retrospective study included 73 cases of neoplasms. Animals older than 9 years of age (49.3%) and females (72.9%) were the most affected. Tumors of epithelial origin were the most common type (53.5%), being mammary adenocarcinoma (21.1%) and lymphoma (16.9%) the most frequent.