Chronic kidney disease (CKD) is a serious condition associated with premature mortality, decreased quality of life, and increased health-care expenditures. Untreated CKD can result in end-stage renal disease and necessitate dialysis or kidney transplantation. Risk factors for CKD include cardiovascular disease, diabetes, hypertension, and obesity. To estimate the prevalence of CKD in the United States (overall and by health risk factors and other characteristics), CDC analyzed the most recent data from the National Health and Nutrition Examination Survey (NHANES). This report summarizes the results of that analysis, which determined that 16.8% of the U.S. population aged >/=20 years had CKD, according to 1999-2004 NHANES data, compared with 14.5% from the 1988-1994 NHANES (i.e., NHANES III), an increase of 15.9% based on crude estimates of prevalence. Persons with diabetes or cardiovascular disease had a greater prevalence of CKD than persons without those conditions. The results underscore the need to continue surveillance for CKD and its risk factors in the United States and to implement new strategies to reduce the number of persons with this condition.