This case of intravascular large B-cell lymphoma (IVLBCL) involving the prostate was discovered incidentally. The patient was an elderly male who presented with urinary retention and underwent transurethral resection of the prostate. The blood vessels were engorged with neoplastic cells throughout the specimen. The tumor cells were positive for CD45, CD20 and Bcl-2. They were negative for CD3, CD43, CD34, PSA, PSAP, and cytokeratin AE1/AE3.