Kidney length (KL), renal area and renal parenchymal area were measured on i.v. urograms of 255 children without apparent kidney disease age 0 to 14 years. These parameters were compared with age, body height, body surface area and the distance between the 1st and 4th lumbar vertebral body. In addition, renal parenchymal thickness was determined at the upper and lower poles. Mean values for normal KL were significantly greater on the left side than on the right side requiring separate growth charts. A mean increase in KL of 6.3 mm for the left and 6.0 mm for the right kidney was calculated for a change of 10 cm body height. A small kidney is defined by a KL below--2 SD for the corresponding body height and/or a quotient of right KL/left KL outside +/- 2 SD from the mean value. Localised loss of renal parenchyma is reflected by an increased or decreased quotient of the upper to the lower polar thickness and reduction of total kidney mass by a diminished bipolar parenchymal thickness related to body height.