A 68-year old patient presented with flank pain caused by a large renal mass. A nephrectomy was performed because renal cell carcinoma was suspected. Pathological examination showed a diffuse large B‑cell lymphoma. Primary renal manifestation of a lymphoma is rare. The diagnosis is often missed or only recognized after a nephrectomy is performed. A primary renal lymphoma must be considered when radiologically a hypovascular, diffuse growing process is seen, without the characteristic signs of renal cell carcinoma, like calcifications and vascular invasion. Diagnosis can be confirmed by biopsies and, once histologically proven, curative treatment with chemo-immunotherapy is possible. In this article the diagnostic considerations and characteristics of a renal lymphoma are described.