A 44-year-old asymptomatic male was incidentally found to have bilateral hydronephrosis in a health examination . Laboratory tests revealed elevated creatinine level (142 μmol/L) in serum and occult blood in urine. Magnetic resonance imaging showed bilateral ureteral thickening with complete obstruction of the right ureter, stenosis of the left proximal ureter and bilateral hydronephrosis, as well as retroperitoneal adenopathy (Fig. 1A and 1B). A routine and delayed (60 minutes after intramuscular injection of furosemide) 18F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) imaging revealed multiple hypermetabolic masses and nodules in the wall of bilateral ureters and para-aortic areas (Fig. 1C–1G). Considering the lesion as a malignancy, a laparoscopic needle biopsy was performed on several hypermetabolic lymph nodes, and histopathological examination revealed follicular lymphoma (Fig. 2). We also performed bone marrow biopsy which did not show lymphoma involvement. After six courses (four cycles of rituximab plus cyclophosphamide, hydroxyldaunorubicin, oncovin and prednisone [R-CHOP] and two courses of bendamustine plus rituximab) of chemotherapy, the patient showed complete resolution on a follow-up ¹⁸F-FDG PET-CT scan (Fig.1H–1K). The patients remained disease-free 2 years after the treatments.