An unexpected association with breast cancer and thyroid disorders was found during a review of 91 cases of benign and malignant ovarian adenofibromas. Sixty-three tumors were benign, 11 had areas of borderline neoplasms, and 17 had a component of carcinoma. Such tumors were divided into glandular/cystic (61 cases) and papillary (30 cases) according to their gross and microscopic appearance. Among the 61 patients with glandular/cystic adenofibromas, 13 (21%) had breast cancer and 19 (31%) also had thyroid disorders. Among the 30 patients with papillary adenofibromas there were no cases of breast cancer and only 2 patients had thyroid disorders. The average age of the patients with ovarian adenofibroma and breast cancer or thyroid disorders was higher (66 years) than that of patients without breast cancer or thyroid disorders (55 years). More patients with breast cancer and thyroid disorders had bilateral adenofibromas than patients without breast cancer or thyroid disorders. We also reviewed the medical records of 100 patients with ovarian cancer without adenofibroma component, 100 patients with breast cancer, and 100 patients with ovarian and breast cancer. Six percent of patients with ovarian cancer had breast cancer and 16% of each one of these groups had thyroid disorders. This unexpected association found between glandular/cystic adenofibromas, breast cancer, and thyroid disorders might be explained by defects common to these organs. Disorders of some of these organs have been linked by common genetic changes and it is known that these organs are under the influence of similar hormones. Mutations of PTEN have been found in breast and thyroid cancer. The thyroid and ovaries are controlled by glycoprotein hormones of the pituitary gland, which have common alpha subunits.