In a 15-year period at the Netherlands Cancer Institute, 17 patients were found with breast carcinoma metastatic to the colon or rectum or both. The presenting symptoms and signs were non-specific and included diarrhea, crampy pain, vomiting, and palpable tumor. Endoscopic examination, possible in only 10 of the 17 patients because of luminal obstruction, yielded a correct diagnosis in seven cases. Biopsy was confirmatory in five cases. Lesions metastatic to the colorectum originated predominantly in lobular carcinoma of the breast. Systemic hormonal or chemotherapy or x-irradiation, either alone or as an adjunct to surgery, produced a favorable response in over half the patients so treated.