Patients with breast carcinoma metastatic to the colon generally present with multiple symptoms, usually pain, vomiting, nausea, and ascites. We describe a patient who presented only with persistent diarrhea, underwent surgery for colon cancer, and, on pathological evaluation of the surgical specimen, was found to have metastatic breast cancer affecting the colon. Metastatic breast cancer should therefore be suspected in patients with a history of breast cancer and diarrhea of unknown cause that is not accompanied by other symptoms. Evaluating such patients by colonoscopy and biopsy would provide important information relevant to choosing between colon surgery and systemic therapy.