Signet ring cell carcinoma of the breast is a rare type of tumor characterized by the presence of numerous cells containing large intracellular and little extracellular amounts of mucin. These tumors show an unusual metastatic pattern, involving serosal surfaces and have a poor prognosis with a mean survival time of 50 months. This paper reports the case of a 39 year old woman with a bilateral signet ring cell carcinoma who developed metastases in bone, lung and peritoneum. Combined surgery, radiotherapy and chemotherapy was used but the patient died 2 years and 3 months after diagnosis.