Human polyomavirus type BK (BKV) associated nephritis (BKVAN) has recently emerged as an important cause of renal allograft dysfunction and failure. Early recognition of this entity as a cause of allograft dysfunction is extremely important since misdiagnosis can accelerate graft loss. We report a case of BKVAN that presented with symptoms related to cystitis, and review the risk factors, the diagnostic tools and the approach to treatment of BK virus associated allograft nephropathy.