Introduction: BKV nephropathy (BKN) causes kidney graft loss, whose specifi c diagnosis is invasive and might be predicted by the early detection of active viral infection. Objective: Determine the BKV-infection prevalence in late kidney graft dysfunction by urinary decoy cell (DC) and viral DNA detection in urine (viruria) and blood (viremia; active infection). Methods: Kidney recipients with >1 month follow-up and creatinine >1.5 mg/dL and/or recent increasing >20% (n = 120) had their urine and blood tested for BKV by semi-nested PCR, DC searching, and graft biopsy. PCR-positive patients were classifi ed as 1+, 2+, 3+. DC, viruria and viremia prevalence, sensitivity, specifi city, and likelihood ratio (LR) were determined (Table 2x2). Diagnosis effi cacy of DC and viruria were compared to viremia. Results: DC prevalence was 25%, viruria 61.7%, and viremia 42.5%. Positive and negative patients in each test had similar clinical, immunossupressive, and histopathological characteristics. There was no case of viremia with chronic allograft nephropathy and, under treatment with sirolimus, patients had a lower viruria prevalence (p = 0.043). Intense viruria was the single predictive test for active infection (3+; LR = 2.8).