The risk of subsequent cytomegalovirus infection (CMV) in kidney transplant recipients (KTR) after diagnosis of BK polyoma-virus viremia (BKV) is unclear, and current evidence is conflicting. We reviewed all KTR transplanted at our institution between 1/1/2005-12/31/2015. Follow-up began 3 months after transplantation to avoid confounding effects of prophylaxis. Clinically significant BKV, defined as detectable BK viremia >1000 copies/mL via molecular diagnostic testing (PCR), was treated as a time-varying exposure with 1 year follow up. This viral load cut off was chosen to ensure a more homogenous population that would be considered to have clinically significant BK viremia that necessitated management via immunosuppressive modification. Patients were then screened for subsequent CMV infection. 2,435 RTX recipients met inclusion criteria; of these, 314 developed BKV during follow-up (BK+). Lymphocyte depletion, tacrolimus maintenance and biopsy proven rejection were significantly higher in the BK+ group. BK+ was associated with lower risk of subsequent CMV infection (BK+ HR 0.45, 95% CI 0.22-0.94, p=0.03, relative risk reduction 55%). When adjusted for significant confounding factors, CMV incidence remained reduced in the BK+ population (HR 0.47, 95% CI 0.22-0.98, p=0.04). This large series of KTR demonstrates that BKV is associated with lower risk of subsequent CMV infection.© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.