To investigate the relationship between age and renal vascular resistance and to establish normative data of the systolic/diastolic ratio (S/D ratio), pulsatility index (PI), and resistant index (RI) of the renal artery in the normal pediatric population, we studied 252 normal children aged newborn to 13 years (a total of 449 kidneys) with a color Doppler unit. After the normality of the kidney was established, color flow mapping was performed to localize the segmental portion of the renal artery. Flow velocity waveforms were then obtained by pulsed Doppler, and S/D ratio, PI, and RI were calculated. Multiple regression analysis confirmed the age dependence of the S/D ratio, PI, and RI of the renal artery in normal children. Renal vascular resistance continuously declines after birth and stabilizes at the age of 102-130 months. Normative data for S/D ratio, PI, and RI of the renal artery in normal children were established for each age group. Since renal vascular resistance decreases with age and stabilizes at 8-10 years, we suggest using different normal ranges for each age group when studying renal vascular resistance in pediatric patients.