This study was undertaken to define the natural history and treatment results of patients with primary breast non-Hodgkin's lymphoma (NHL). Twelve female patients who had been followed at Hacettepe University Hospital between 1973 and 1997 were retrospectively evaluated. All patients presented with breast masses (6 in the right breast and 6 in the left) that had recently enlarged. The most common histologic subtype was diffuse, small cleaved-cell lymphoma. Chemotherapy regimens were employed in 9 patients. Radiotherapy was delivered to the breast and its lymphatics in 8 patients. Lumpectomy, simple or modified radical mastectomy was performed in 5 cases. An objective response was attained with surgery, chemotherapy, or radiotherapy alone in 2, 1, and 1 cases, respectively. Combined modality treatment including either two or three modalities was successful in 7 cases. The median progression-free and overall survival times were 49 and 56 months, respectively. Although primary NHL of the breast is a rare disease compared to carcinoma, it should be considered in the differential diagnosis of breast masses.