The signet ring variant of lobular mammary carcinoma is aggressive and metastastises to serosal surfaces. We report a 46 years old woman presenting with an intestinal obstruction due to a peritoneal carcinomatosis secondary to a signet ring cell carcinoma of the breast. After surgery, the patient received chemotherapy (5-fluorouracil, adriamycin, cyclophosphamide and tamoxifen). A satisfactory response, with regression of peritoneal carcinomatosis and a good quality of life, was achieved. The patient is alive after 2 years of diagnosis.