BACKGROUND AND OBJECTIVES: Conflicting data have been reported concerning the use of kidney graft arterial resistance index (RI) measured by Doppler to predict death-censored graft loss. We hypothesized that changes in RI values could carry better information than a single measure of RI. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Four hundred twenty-five renal transplant recipients were included in the study. We tested whether changes in renal arterial resistance index between 4 and 12 months after transplant (DeltaRI(4-->12)) were predictive of graft loss. RESULTS: Neither 4-month nor 1-year RI predicted graft loss. The area under the receiver operating characteristics curve of DeltaRI(4-->12) for graft loss was 0.75. A DeltaRI(4-->12) >/=10% had the best sensitivity and specificity. One year after transplant, 22% of the study population had DeltaRI(4-->12) >/=10%. Fifty-five patients (12.9%) experienced graft loss during follow-up. The annual incidence of graft loss was higher in patients with DeltaRI(4-->12) >/=10% (3.5 versus 1.3%; P = 0.009). In multivariate analysis, patients with DeltaRI(4-->12) >/=10% had an increased risk of graft loss (hazard ratio, 6.21; 95% confidence interval, 1.99 to 22.15; P = 0.002). CONCLUSIONS: A variation in RI >/=10% in the first year after transplant is an independent risk factor for death-censored graft loss in renal transplant recipients.