We sought to examine the impact of asymptomatic bacteriuria on renal transplant outcome by retrospectively analyzing 189 renal transplant recipients for whom systematic screening uncovered 298 episodes of asymptomatic bacteriuria in 96 recipients. These patients were treated and all were followed for 36 months. Significant risk factors included female gender, glomerulonephritis as the disease that led to transplantation, and double renal transplant. There were no differences in serum creatinine, creatinine clearance, or proteinuria between patients with and without bacteriuria. The incidence of pyelonephritis in these patients was 7.6 episodes per 100 patient-years compared with 1.07 in those without asymptomatic bacteriuria. Between two to five and more than five bacteriuria episodes were significant independent factors associated with pyelonephritis whereas more than five episodes was a significant independent factor associated with rejection. Thus, we found no differences in renal function prognosis between patients who do not develop asymptomatic bacteriuria and those uncovered by systematic screening and who received treatment following kidney transplantation. Despite this treatment, the incidence of pyelonephritis was much higher in the group of patients with detected asymptomatic bacteriuria.