We evaluated the estrogen receptor (ER) phenotype of recurrent and/or metastatic breast cancers and compared it with the ER status of the primary tumor in 278 cases. All patients had undergone surgical excision of the primary tumor, followed by observation only or treatment modalities that included radiation and/or chemotherapy or hormonal therapy. The immunohistochemical expression of ER was evaluated by using monoclonal antibody ER-1D5 and heat-induced antigen retrieval. At diagnosis, 165 patients had locoregional disease and 7 had distant metastases. Local recurrences and/or distant metastases occurred from 2 months to 21 years after the diagnosis of the primary tumor. Overall, 159 primary tumors (57.2%) were positive for ER. In 269 cases (96.8%), the ER status of the primary and metastatic tumors was the same. In 9 patients with ER+ primary tumors, the metastases were ER-. There were no ER- primary tumors with ER+ metastases. The time to distant metastasis was significantly longer for ER+ tumors. The immunohistochemically determined ER phenotype of primary breast cancers remains stable in most recurrent and metastatic disease.