Post-mortem written protocols (including histopathology slides) from necropsies performed on 3211 canines in the Histopathology Laboratory of Faculty of Veterinary Medicine, San Marcos University between 1973 and 1999 were analyzed. Ofthis total, neoplasic lesions were found in 693 (21.21 %) cases, including 147 (3.11 %) mammary tumors. Among the fema le canines, mammary tumors comprised 40. 83 % ( 14 7 /3 60) of ali neoplasias, including 90 cases ofadenocarcinoma, and were more conunon in animals aged 6 years or greater. Incidence among breeds was: Pug (33.33%), Dachshund (25%), Terrier (28.57%), and Cocker Spaniel (28.13%).