Plasmablastic lymphoma (PBL) is a rare and aggressive subtype of B-cell lymphoma, which occurs typically in the oral cavity of human immunodeficiency virus (HIV)-positive patients. We report a case of a 44-year-old HIV-positive patient with a solitary polypoid mass of the left ureteropelvic junction, causing unilateral hydronephrosis and clinically mimicking urothelial carcinoma. A laparoscopic nephroureterectomy was performed, and pathological examinations revealed the mass as PBL. PBL can present in various forms, even as a polypoid mass of the upper urinary tract, and it should be considered in the differential diagnosis of any mass detected in the HIV-positive patients.

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