Differentiating acute tubular necrosis (ATN) from prerenal azotemia is critical for selecting the appropriate treatment. This study was conducted to evaluate the diagnostic value of Doppler ultrasonography in differentiating ATN from prerenal azotemia in children. A total of 50 oliguric or anuric children with previous normal renal laboratory data were included. Doppler examination and calculation of resistive index (RI) was performed within 24 hours of admission and in the recovery phase of ARF. The sensitivity and specificity of RI in differentiating ATN from prerenal azotemia were assessed. At the cut-off point of RI = 0.75, the sensitivity and specificity of RI in differentiating prerenal failure and ATN was 91.3% and 85.2%, respectively. We conclude that Doppler ultrasonography is helpful in differentiating ATN from prerenal azotemia in children. The cut-off value of 0.75 has the highest accuracy for this purpose.