A retrospective review was conducted to determine the incidence, etiology, natural history and complications of hyperuricemia after pediatric renal transplantation. Of 81 active transplant recipients aged 10.1 +/- 4.8 (mean +/- SD) years being followed by St. Christopher's Hospital for Children, 57 (70%) were males and 59 (73%) Caucasian. Their immunosuppression consisted of azathioprine, cyclosporine A and prednisone. Mean serum uric acid concentrations peaked at 6 months post transplantation (6.2 +/- 2.6 mg/dl), when 39% of the patients had hyperuricemia and 60% were receiving diuretics, and decreased thereafter. At 30 months, 23% of the patients had hyperuricemia and 17% required diuretics. When we compared 42 normouricemic (group A) with 24 hyperuricemic (group B) patients at 18 months post transplantation, we found that patients in group B were older (11.6 +/- 4.2 vs. 8.6 +/- 5.2 years, P = 0.01), had worse renal function (77 +/- 25 vs. 96 +/- 36 ml/min per 1.73 m2, P = 0.03) and required diuretics more frequently (63% vs. 21%, P = 0.001), but had identical blood levels of cyclosporine A (82 +/- 28 vs. 84 +/- 35 ng/ml, P = 0.78). A family history of gout did not affect the prevalence of hyperuricemia after transplantation. Asymptomatic hyperuricemia is common following pediatric renal transplantation and is more likely attributable to reduced renal function and diuretic therapy than to the known hyperuricemic effect of cyclosporine A. Of these variables, only diuretic therapy is readily controllable and should be closely regulated following pediatric renal transplantation.