We report three cases of malignant lymphoma (ML) of the breast and discuss diagnosis and management. The first case is a 35-year-old woman who had a left breast tumor. Fine needle aspiration cytology (FNAC) showed ML. Mastectomy was performed without any adjuvant chemotherapy. Histology revealed diffuse large B-cell lymphoma of REAL classification. Seventy one months after surgery, lesions indicating relapse were detected in nodes of the right axilla, mediastinum and para-aorta. She underwent eight cycles of CHOP regimen, but 1 month after the chemotherapy a brain metastasis was detected. The patient then received a high-dose methotrexate regimen with whole-skull irradiation. The second case is a 47-year-old woman who had anterior neck swelling and bilateral breast tumors. Histology of the tumor revealed diffuse large B-cell lymphoma. The patient underwent eight cycles of CHOP regimen and high-dose chemotherapy (HDC) with peripheral blood stem cell transplantation (PBSCT). Forty eight months after the PBSCT, there is no evidence of disease. The third case is a 38-year-old woman who had a right breast tumor. FNAC of the breast tumor showed ML and a CT scan of the chest revealed lymphadenopathy at the crus of the diaphragm. Histology of the tumor revealed low-grade B-cell lymphoma of MALT type. The patient underwent six cycles of CHOP regimen and HDC supported by PBSCT. Eighteen months after the PBSCT, relapse lesions were detected in nodes of the neck, mediastinum and renal hilum. The patient received nine cycles of a THP-COP regimen.