Abstract: The present application describes and claims a novel method for identifying and stratifying the risk of developing a BK virus nephropathy (“Nx BK-v” below) in patients having undergone a kidney transplant. This method uses an index combining at least three bio-markers: i) the intensity of the anti-BK-v memory T lymphocyte response (memory T lymphocytes which are specific to v, hereinafter “LTm anti-BK-v”), ii) the number of occurrences of incompatibility in the HLA alleles of class I and class II between the donor and the recipient of the graft, taking into account iii) the viral charge of the BK-v virus in the whole blood of the patient. The present method allows a very precise evaluation of the risk of developing an Nx BK-v during the months following the test with the aim of optimising the immuno-suppressive treatment in order to better preserve the transplanted kidney.