Here we report a case of a 73-year-old man with primary intravascular large B-cell lymphoma localized to the prostate. Total prostatectomy was performed due to a benign adenoma suggested by ultrasonography. The diagnosis of IVLBL was obtained incidentally from the prostatectomy specimen. Eight months after the initial R-CHOP chemotherapy a relapse was detected in the left inguinal lymph node, where histologic examination revealed common diffuse large B-cell lymphoma with minimal intravascular component. The second complete remission was achieved by R-IEV therapy. Five months later a second relapse occurred and the patient died in the widespread disease and pneumonia. Primary prostate IVLBL is extremely uncommon; to date only four cases have been described. This is a well documented case, where we also confirmed that the initial primary IVLBL and the secondary lymph node involvement are clonally related. Successful treatment depends on early diagnosis of IVLBL, aggressive chemotherapy and the fact that IVLBL should be considered as a generalized disease in spite of negative staging results.