More than 20 years after its first description and increased morbidity under powerful immunosuppression, the understanding of the pathogenesis of BK polyomavirus induced allograft nephropathy (BKVN) has changed clinical practice in renal transplantation. Screening programs were introduced at most transplant centers causing the prevalence of BKVN to decrease. However, BK viremia is still found in 10-30% of renal allograft recipients with 1-10% developing BKVN. This article is protected by copyright. All rights reserved.