BACKGROUND: Hyperuricemia has been reported to affect renal hemodynamics. In a recent study, both low and high levels of serum uric acid (SUA) were found to be associated with loss of kidney function. Objective: The goal of this study was to evaluate the relationship between SUA levels and intrarenal hemodynamic parameters in healthy subjects, utilizing plasma clearance of para-aminohippurate (CPAH) and inulin (Cin). Subjects and Methods: Glomerular hemodynamics were evaluated by CPAH and Cin in 48 healthy subjects (54.6 ± 13.4 years). Intrarenal hemodynamic parameters, including efferent (Re) and afferent (Ra) arteriolar resistance, were calculated using Gomez's formulae. Relationships of SUA levels with these intrarenal hemodynamic parameters were examined. Results: In quadratic regression analysis, SUA levels had a significant, inverse U-shaped relationship with Cin (p < 0.0001, R2 = 0.350) and CPAH (p = 0.0093, R2 = 0.188), and a U-shaped relationship with Ra (p = 0.0011, R2 = 0.262). In multiple regression analysis with normal (3.0 to 6.0 mg/dL) and mildly low or high (<3.0 or >6.0 mg/dL) SUA levels entered as dummy variables of 0 and 1, respectively, mildly low or high SUA levels were significantly and independently associated with Ra (β = 0.230, p = 0.0403) after adjustment for several factors (R2 = 0.597, p < 0.0001). Conclusions: Both mild hyperuricemia and mild hypouricemia are significantly associated with increased Ra; albeit weakly. The increase in Ra in subjects with mild hyperuricemia or hypouricemia may cause renal hemodynamic abnormalities, possibly leading to a decline in renal function.