To evaluate renal tubular function in young insulin dependent diabetics.Plasma uric acid levels, renal urate excretion, uric acid tubular load and uric acid fractional excretion were compared between a group of young diabetics without microalbuminuria (n = 27), between 5.5 and 16.8 years of age, and a control group (n = 22).The plasma uric acid levels was lower in the diabetic group than in the control group (2.9 +/- 0.7 vs 3.6 +/- 0.6 mg/dl). The renal excretion of urate was higher in the diabetic group than in the control group (17.6 +/- 4.8 vs 13.6 +/- 5.1 mg/kg/d). The uric acid tubular load was similar in both groups (2.5 +/- 1.0 vs 2.4 +/- 0.7 mg/min/1.73 m2). The uric acid fractional excretion was higher in the diabetic group than in the control group (20.9 +/- 11.9 vs 11.4 +/- 4.8%). No correlation between plasma uric acid level and renal urate excretion with insulin therapy (U/kg/d), metabolic control or the time of evolution was found.These results suggest that, in young diabetics, there is a renal hypouricemia due to tubular defects.