Primary lymphoma of the breast is very rare especially in a male patient. Treatment alternatives include surgery, chemotherapy, immunotherapy and radiation. It is still controversial which combination is the best. Here, we report a male patient who presented with a left breast mass. The excisional biopsy was applied, and pathological assessment revealed marginal zone lymphoma. Both conventional computed tomography and 18) F-Fluorodeoxyglucose positron emission tomography/computed tomography were used for staging. The clinical stage was IIE for Ann Arbor staging and so local radiation following chemo immunotherapy was planned. Left-sided primary breast lymphoma in a male patient is a very rare entity. Treatment modalities are still controversial. Some authors believe that primary breast lymphomas have poor prognosis, and they must be treated aggressively with combined treatment modalities. Another important point is that 18) F-Fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET)/CT could be used for staging of disease and assessing treatment response in a patient with primary breast marginal zone lymphoma.