The incidence of kidney failure treatment in the United States increased 57% from 1991 to 2000. Chronic kidney disease (CKD) prevalence was 11% among U.S. adults surveyed in 1988 to 1994. The objective of this study was to estimate awareness of CKD in the U.S. population during 1999 to 2000 and to determine whether the prevalence of CKD in the United States increased compared with 1988 to 1994. Analysis was conducted of nationally representative samples of noninstitutionalized adults, aged 20 yr and older, in two National Health and Nutrition Examination Surveys conducted in 1988 to 1994 (n = 15,488) and 1999 to 2000 (n = 4101) for prevalence +/- SE. Awareness of CKD is self-reported. Kidney function (GFR), kidney damage (microalbuminuria or greater), and stages of CKD (GFR and albuminuria) were estimated from calibrated serum creatinine, spot urine albumin to creatinine ratio (ACR), age, gender, and race. GFR was estimated using the simplified Modification of Diet in Renal Disease Study equation. Self-reported awareness of weak or failing kidneys in 1999 to 2000 was strongly associated with decreased kidney function and albuminuria but was low even in the presence of both conditions. Only 24.3 +/- 6.4% of patients at GFR 15 to 59 ml/min per 1.73 m(2) and albuminuria were aware of CKD compared with 1.1 +/- 0.3% at GFR of 90 ml/min per 1.73 m(2) or greater and no microalbuminuria. At moderately decreased kidney function (GFR 30 to 59 ml/min per 1.73 m(2)), awareness was much lower among women than men (2.9 +/- 1.6 versus 17.9 +/- 5.9%; P = 0.008). The prevalence of moderately or severely decreased kidney function (GFR 15 to 59 ml/min per 1.73 m(2)) remained stable over the past decade (4.4 +/- 0.3% in 1988 to 1994 and 3.8 +/- 0.4% in 1999 to 2000; P = 0.23). At the same time, the prevalence of albuminuria (ACR >/= 30 mg/g) in single spot urine increased from 8.2 +/- 0.4% to 10.1 +/- 0.7% (P = 0.01). Overall CKD prevalence was similar in both surveys (9% using ACR > 30 mg/g for persistent microalbuminuria; 11% in 1988 to 1994 and 12% in 1999 to 2000 using gender-specific ACR cutoffs). Despite a high prevalence, CKD awareness in the U.S. population is low. In contrast to the dramatic increase in treated kidney failure, overall CKD prevalence in the U.S. population has been relatively stable.