Patients with insulin-dependent diabetes mellitus and poor glycemic control show hypouricemia with hyperuricosuria. In the present study, we have evaluated whether a good glycemic control influences the renal handling of uric acid. Sixteen patients (8 male, mean age 22.4 +/- 7.2 years) were studied under two situations, poor glycemic control (glycemia > 11 mmol/L and HbA1 c > 10%) and good glycemic control (glycemia < 6 mmol/L and HbA1 c < 8.5%). A group of 16 normal subjects served as the control group (8 male, mean age 21.9 +/- 9.1 years). In the poor glycemic control phase, patients showed lower plasma uric acid levels (0.18 +/- 0.06 mmol/L) and higher fractional urinary excretion of uric acid (16.1 +/- 9.3%) than the controls (0.28 +/- 0.06 and 8.2 +/- 1.9%, respectively). When a good glycemic control was reached, plasma uric acid increased (0.22 +/- 0.05), but it was still lower than that of the controls and fractional excretion of UA was normalized. Plasma uric acid was inversely correlated to glycemia (r = -0.34, p < 0.05) and to HbA1 c (r = -0.56, p < 0.0008) and fractional excretion of uric acid was directly correlated to glycemia (r = 0.39, p < 0.03) and HbA1 c (r = 0.73, p < 0.00005). These results indicate that the hypouricemia and hyperuricosuria of insulin-dependent diabetes mellitus is corrected by an adequate glycemic control, suggesting that these alterations are of a functional origin and due to a defective metabolic control.