Résumé : Polyomavirus (PV) is a major cause of kidney graft disease. Monitoring by polymerase chain reaction (PCR) on blood is currently recommended. In order to avoid irreversible lesions, we investigated the clinical impact of preemptive reduction of immunosuppression (IS) in kidney transplant recipients (KTR) upon detection of high urinary PV (Upv) load, including BK virus and JC virus.