Limited data are available concerning treatment and outcome of primary lymphoma of the breast (PLB), especially after CHOP (cyclophosphamide, hydroxydoxorubicin, vincristine, prednisone) chemotherapy. We retrospectively reviewed 20 consecutive cases of localized PLB seen at our institution over a 20 year period. All PLB were of B-cell origin: treatment was CHOP or a CHOP-like regimen in all patients. Sixteen of the 20 patients achieved complete remission (CR) and two achieved partial remission (> 75% tumour regression). Two patients had progressive disease on therapy. With a median follow-up of 54 months, six patients relapsed after 8-66 months. Two of the relapses involved the central nervous system (CNS) (isolated in one case, associated with other sites of relapse in the other). The two patients who achieved partial remission also had progression in the CNS, 4 and 8 months after the end of CHOP chemotherapy. All four patients have died as a result of their disease 3, 6, 10 and 13 months after CNS relapse. Of the 16 centroblastic diffuse large B-cell lymphoma (DLCL), three had CNS disease at relapse. We also observed three (15%) controlateral breast relapses. Thirteen of the initial 20 patients are alive in CR, six patients have died as a result of their lymphoma and one of unrelated disease. In conclusion, we observed a high incidence of CNS relapse in this group of localized extranodal lymphoma, strongly suggesting that CNS prophylaxis should be associated with systemic chemotherapy in localized PLB.