Microalbuminuria (MA) is an important early sign of diabetic nephropathy. Hyperfiltration and impaired filtration in relation to albuminuria has been well investigated in diabetic subjects. This study tested the hypothesis that an increased urinary albumin excretion (UAE) is associated with renal functional abnormalities also in nondiabetic subjects. The relation between UAE and creatinine clearances (Ccr) in 7728 nondiabetic subjects was studied. Subjects were divided in four groups according to UAE (mg/24 h): 0 to 15 (control), 15 to 30 (high-normal albuminuria [HNA]), 30 to 300 (MA), >300 (macroalbuminuria). An elevated filtration and a diminished filtration were defined as a Ccr exceeding or below 2x the SD of the control group corrected for age and gender. Ccr followed a parabolic trend, with a higher Ccr in the HNA as compared with control and a lower Ccr in the MA and macroalbuminuria group as compared with HNA. With each increasing UAE level, male sex, age, body mass index, minimal waist circumference, systolic and diastolic BP, plasma glucose, and a positive family history for diabetes all followed a significant linear increasing trend (P < 0.001). After adjustment for age, gender, body mass index, plasma glucose, a positive family history for diabetes, systolic and diastolic BP, antihypertensive medication, and smoking in a multivariate analysis, HNA and MA were independently associated with an elevated filtration (RR 1.8 [95% confidence interval, 1.30 to 2.51] and 1.7 [1.17 to 2. 45]). Macroalbuminuria was independently associated with a diminished filtration (4.3 [range, 1.97 to 9.36]). In conclusion, an elevated UAE might be an important and early sign for progressive renal function loss in a nondiabetic population.