The renal arteries of 62 children and adolescents aged 1–16 year without renal or renovascular disease were examined by computer Doppler duplex sonography (DDS) to measure absolute renal blood flow velocities. Maximum systolic velocity (V_max) and time average velocity (TAV) were not age-dependent. In addition, absolute values of renal artery and renal blood flow were measured. Renal blood flow was 4.1±1.2 ml/min per gram kidney (two standard deviations), independent of age and comparable to commonly accepted physiological values. The coefficient of variation of blood flow calculations was 6%–15% depending on vessel diameter.