Signet-ring cell carcinoma (SRCC) can arise from virtually all organs. However, primary SRCC of the breast is very rare. Until 2003, SRCC was placed under 'mucin-producing carcinomas' and separated from other carcinomas by the World Health Organization (WHO). To date, only a few cases have been reported. A case of a 46-year-old woman with primary SRCC of the breast is presented in this report. The patient underwent a right modified radical mastectomy with axillary lymph node dissection. Characteristic features and differential diagnosis of this tumor are discussed in the light of pertinent literature.