Diminished glomerular filtration rate, proteinuria, and large hypercellular congested glomeruli with segmental sclerosis are found in late survivors with cyanotic congenital heart disease (CCHD). Hyperuricemia is common, acute gouty arthritis is less common than uric acid levels would predict, and overt tophaceous deposits of uric acid are exceptional. The role of the kidney in causing the basic biochemical disturbances, and the relative importance of impaired urate excretion vs urate overproduction have not been established. Accordingly, we reviewed the courses of two index patients and prospectively studied eight additional CCHD patients from 28 years to 46 years old with mean hematocrits of (62 ± 10%). Plasma creatinine concentration was normal (0.9 ± 0.1 mg/dl) yet glomerular filtration rate was mildly reduced to 93 ± 14 ml/min as measured by creatinine clearance and to 81 ± 6 ml/min as measured by111In DTPA. Three patients had significant proteinuria and one was nephrotic. Plasma uric acid concentration was high in all but one (8.2 ± 2.1 mg/dl), mean 24 hr uric acid excretion was normal (564 & 221 mg), and fractional uric acid excretion was relatively low (6.3 ± 2.6%). The two patients with highest plasma uric acid levels (12.0 and 10.2 mg/dl) had the lowest fractional excretions (2.8% and 4.0%). Both of these patients had diminished capacity to excrete a water load (38% and 27%/4 hr) and to maximally concentrate urine (520 and 635 mOsm/kg after water deprivation and vasopressin). In conclusion, high plasma uric acid levels in late survivors with CCHD are secondary to inappropriately low fractional uric acid excretion, not to urate overproduction. Hyperuricemia serves as a marker of abnormal intrarenal hemodynamics. Enhanced urate reabsorption appears to result from renal hypoperfusion reinforced by a high filtration fraction.