Background. BK virus nephropathy is the most common type of viral disease to occur following renal transplantation. Although its frequency differs according to transplantation center, the rate is between 1.5% and 20%. Diagnosis can be established histologically by renal allograft biopsy. The aim of this study was to determine the frequency of BK virus nephropathy in patients who had had a renal biopsy for graft dysfunction at our center.