Although malignant lymphoma of the breast is a rare disease, we recently experienced a high incidence of central nervous system (CNS) involvement. Thus, we retrospectively reviewed clinical records of 921 patients with breast tumors, treated from 1990 to 2002, to examine CNS involvement. Eight patients were found to have malignant lymphomas during this period. Of these, four patients ranging from 46 to 80 years of age had CNS involvement, one with Burkitt type and three with diffuse large B-cell lymphoma. The patients received surgery and/or chemotherapy and/or radiotherapy. The four other patients without CNS involvement are alive without tumor, whereas three of four patients with CNS involvement died of the disease. It should be noted that CNS involvement in breast lymphoma is not so rare. It is difficult, but important, to determine whether malignant lymphoma of the breast originates in the breast or is of systemic origin. Although brain metastasis could be treated effectively by radiotherapy and/or chemotherapy, the prognosis was poor. Further intensive treatment is required for breast malignant lymphoma with CNS involvement.