Mammary tumors are one of the most common neoplasms presented in the bitch; in a large number of cases, hormonal receptors were demonstrated in neoplastic cells and, that the growth is hormone-dependent. Most of these hormones are produced in the ovary. This work was to evaluate the risk that a bitch with a mammary tumor also presents alterations in its ovaries. The morphologic condition of the ovaries from 200 bitches older than 7 years were studied. Of the 200, 50 had mammary tumors. The measure of risk and its significance level were analyzed. Of the bitches with mammary tumors, 20 (40%) presented ovarian alterations, mainly ovarian cystic and cyst adenoma. Only one ovarian alteration was noted in those animals that did not show mammary neoplasia. The risk = 16 (p <0,01) and indicates that in a high percentage of bitches the ovarian alterations might be due to mammary tumors. Given that, those dogs that have mammory tumors possess a risk of having ovarian abnormalities 16 times greater than those presenting without mammary tumors. We advice ovariectomy at the same time as removal of the mammary tumor to avoid later problems.