We present a patient with relapse of B-cell non-Hodgkin's lymphoma in the breast that was clinically presented as a primary breast cancer. A 72-year old female was treated with chemotherapy and monoclonal antibodies (anti-CD20) due to diffuse large B-cell non-Hodgkin's lymphoma. Complete remission was achieved. Three years later, she was presented with a palpable left breast lump in the perimammillar area of the left breast, dimensions up to 3 cm. Laboratory results were within normal range. Mammography re-vealed a solitary, bilobulated, non-calcified mass of the left breast. On ultrasound, the lesion was hypo-echoic with blurred edges, with posterior acoustic enhancement, measuring 2 × 3 × 7 × 2 cm. Histological findings of ultrasound-guided fine needle aspiration and core needle biopsy were corre-spondent to diffuse large B-cell lymphoma. Pathohistological report showed cells with CD20+/Bcl- 2+/Bcl-6-/MUM-1+/CD3- imunophenotype. The breast parenchyma was infiltrated with B-cell lym-phoma. After diagnosis was confirmed, radiotherapy was initiated. Repeat ultrasound studies showed complete regression of the left breast lesion as did positron emission tomography- computed tomography (PET/CT) scan three months after therapy. In conclusion, the relapse of lymphoma in the breast is very rare. In patients previously treated for lymphoma, differential diagnosis should always include relapse, although it clinically presents itself as a primary breast cancer