Diseases of the female reproductive tract in dogs have varying degrees of morbidity and mortality and are directly related to the influence of reproductive history and previous pharmacological treatments, as well as environmental conditions, which can lead to regional variations in the incidence of certain reproductive abnormalities. Ovarian dysfunctions, especially problems involving polycystic ovaries, are some of the causes of infertility in domestic animals. These alterations are frequently found in cows, and sometimes reported in dogs. This paper describes a case of ovarian pathology in an 11 year-old bitch that was taken to the veterinary hospital at the Universidade Federal Rural da Amazonia Ufra, Belem, Para, Brazil, with evidence of a mammary tumor of approximately 20 cm in diameter. The tumor was removed and an OSH was carried out, making it possible to verify that both ovaries were polycystic. However, the right organ presented somewhat unusual dimensions: 8.5 cm in height, 19 cm in width, 23 cm in length, and 2.2 kg in weight. These clinical findings and histopathology were used to diagnose a case of ovarian polycystic disease. Rev. Ci. Agra., v.53, n.2, p.212-215, Jul/Dez 2010 doi: 10.4322/rca.2011.030