We describe the clinical, radiological, and pathological findings of the diverse benign and malignant breast neoplasms found in association with Cowden syndrome. Patients with Cowden syndrome had a substantially increased risk of breast carcinoma. We find that 33% of the patients in our study population with Cowden disease have developed breast carcinoma to date. An association between Cowden disease and multiple tubular adenomas or breast hamartomas was found in two patients, suggesting a genetic origin. PTEN germ-line mutations were found in all four patients presenting with relevant benign or malignant breast pathology. We also assess the value of specific diagnostic tools used in the surveillance management. Screening mammography was useful in the diagnosis of small, high-grade carcinomas.