Primary lymphoma of the breast is rare, accounting for 1.7-2.2% of extranodal lymphomas and 0.38-0.7% of non-Hodgkin's lymphomas (NHL). The aim of this study was to evaluate the clinicopathological features and treatment outcomes of patients with primary breast lymphomas (PBL). We conducted a retrospective review of the NHL cases diagnosed at Korea Cancer Center Hospital between 1989 and 2002. Nine (0.9%) of the 1,050 cases fulfilled the criteria for PBL. All patients were women (median age, 45 years) and usually presented with breast masses that had recently become enlarged. Six cases involved the breast alone (stage IE), whereas 3 cases also involved the ipsilateral axillary lymph nodes (stage IIE). Histopathologic studies revealed a diffuse large B cell lymphoma in 7 cases, marginal zone B cell lymphoma in 1 case, and small lymphocytic lymphoma in 1 case. Immunohistochemical analysis revealed a B-cell phenotype in all cases. There was no uniform approach to the treatment of PBL. Modified radical mastectomy and chemotherapy was performed in 4 cases, modified radical mastectomy and chemoradiotherapy was performed in 1 case, chemoradiotherapy alone, modified radical mastectomy alone, chemotherapy alone, and radiotherapy alone were performed in 1 case each. All cases achieved complete remission, but median overall survival was 12 months, showing very poor prognosis irrespective of the type of treatment modality.