Purpose of reviewIn 1995, BK virus (BKV) surfaced as a significant opportunistic pathogen, causing polyomavirus-associated nephropathy (PAN) in kidney transplant (KTX) recipients. This review, based on data published in 2002–2003, provides an update on the role of BKV in solid organ transplant (SOT) recipients.Recent findingsIn heart and liver transplant recipients, urinary BKV shedding and low-level viremia has been detected without disease. In solitary pancreas transplantation, one case of PAN has been identified among 4/38 (11%) of patients with BKV replication in the urine, which was associated with higher levels of tacrolimus. In KTX recipients, multiorgan failure due to vasculopathy and urothelial carcinoma represent exceptional manifestations of BKV disease. However, PAN is now recognized as a persisting complication affecting 1%–8% of KTX patients. Although the emergence of PAN coincided with the introduction of tacrolimus and mycophenolate into clinical practice, risk factors are not unequivocally defined. Reducing immunosuppression represents the primary mode of intervention, but validated intervention protocols are lacking. Screening for BKV replication in urine, plasma or protocol biopsies favors an earlier diagnosis of PAN with improved response to intervention. Case series using low-dose cidofovir show promising results, especially when combined with modified immunosuppression. Possibly, new immunosuppressive drugs with anti-proliferative or antiviral activity may enable interruption of the vicious circle of rejection and PAN. Retransplantation is an option in the management of PAN with recurrence documented in only 2/11 cases.SummaryBKV replication is frequently found in SOT recipients, but disease is largely limited to the kidneys. The preferential manifestation of PAN in KTX emphasizes the allo-situation in addition to immunosuppression. BKV screening of KTX patients is warranted to enable early intervention. Large prospective studies are needed to identify risk factors and to evaluate intervention strategies for PAN.