<p>Intravascular large B-cell lymphoma (IVLBCL) is a rare and aggressive subtype of extranodal large B-cell lymphoma, characterized by the confinement of tumor cells within the lumens of small blood vessels. It most commonly involves the skin, central nervous system, bone marrow, liver, and spleen, with primary involvement of the prostate being particularly rare. This article reports a case of a 71-year-old male patient who presented with progressive urinary difficulty. Imaging suggested severe prostatic hyperplasia, and benign prostatic hyperplasia (BPH) was considered preoperatively. However, histopathological examination of the prostate after transurethral resection revealed numerous proliferating neoplastic lymphocytes within the prostatic blood vessels. The diagnosis of primary prostatic intravascular large B-cell lymphoma was confirmed by immunohistochemistry and molecular pathology and PET-CT scans. The patient received first-line ZR2 chemotherapy (rituximab + lenalidomide + zanubrutinib). However, he developed acute liver failure during the second cycle, which improved after treatment. The patient has survived for 23 months during follow-up. Primary prostatic IVLBCL is clinically rare and often misdiagnosed as a benign condition due to the lack of specific symptoms. Early biopsy and immunohistochemistry are crucial for accurate diagnosis.</p>