Renal length was measured from normal real-time sonograms of 203 pediatric patients and graphed to provide a "growth chart" of normal renal size vs. age. Mean renal lengths are reported for each year of age. For children older than 1 year, the regression equation is: renal length (cm) = 6.79 + 0.22 X age (years). For babies younger than 1 year, the equation is: renal length (cm) = 4.98 + 0.155 X age (months).