To assess the accuracy of renal function quantification with Tc 99m-DMSA in children, we compared DMSA renal uptake and creatinine clearance in 16 cases of children with single kidney. The age of the patients ranged from two month to fourteen years. DMSA renal uptake was measured 7 hours after injection and was normalized in percent of the injected activity. A significant correlation was found between creatinine clearance and DMSA uptake (Pearson's r = 0.866, p less than 0.01). Normal creatinine clearance in children (80 to 120 ml/min-1 X 1.73 m-2) allowed determination of normal renal uptake (36 to 60%). This study indicates that in cases of asymmetrical renal impairment renal uptake reflects split renal creatinine clearance. Since the former is much easier to measure, DMSA should play an important role in the evaluation of differential renal function.