OBJECTIVE BK virus infection after transplantation is known to cause graft failure but the association with malignancies is controversial. METHODS BK virus workup was performed for kidney recipients in our center under conditions of hematuria or acute deterioration of graft function. We reviewed the history and reported our treatment and the disease course of three patients with BK virus later diagnosed with urothelial carcinoma. RESULTS All three patients received kidneys from China with immunosuppression using a calcineurin inhibitor and monoclonal antibodies. Synchronous bladder and upper-tract tumors were treated with surgery followed by intravesical chemotherapies. We tapered the immunosuppressants and changed to a sirolimus-based regimen. Intravesical chemotherapy and concurrent chemoradiotherapy were performed to prevent recurrence. All three patients now have functional grafts. CONCLUSION BK virus infection may lead to tumorigenesis. Besides decreasing immunosuppressants, we should be more alert to the detection of malignancies in BK virus-reactivated recipients. Early aggressive treatment may be curative, preserving functional grafts.