Anemia associated with chronic renal insufficiency (CRI) may have substantial clinical and public health importance, butlittle is known about its epidemiology.This study aims to quantify the relationship between reduced renal function and hemoglobin level, to assess the iron status of subjects with CRI, and to estimate the burden of anemia associated with CRI.The Third National Health and Nutrition Examination Survey (NHANES Ⅲ) (1988 to 1994) data on 15,971 adults aged >18 yr with measurements of serum creatinine, hemoglobin, and iron profile were analyzed.General linear models were used to determine the relationship between hemoglobin level and Cockcroft-Gault creatinine clearance (CrCl) and to estimate the likelihood of anemiaat different levels of renal function in different demographic subgroups.Sample weights were used to produce weighted regression parameters and population estimates.A statistically significant decrease in hemoglobin was apparent among men starting at CrC1 ≤70 ml/min and among women starting at CrCl ≤50 ml/min.At any given level of CrCl, men had a larger decrease in hemoglobin than women.For example, compared with subjects with CrCl >80 ml/min, the decrease in hemoglobin for subjects with CrC1 20 to 30 ml/min was 1.0 g/dl in women and 1.4 g/dl in men.A substantial number of subjects with CRI might not have sufficient iron stores to support erythropoiesis as judged by the NKF-K/DOQI transferrin saturation or serum ferritin targets.Among those with CrCl 20 to 30 ml/min, 46% of women and 19% of men had transferrin saturation <20%, and 47% of women and 44% of men had serum ferritin <100 ng/ml.Results estimate that 13.5 million US adults had CrCi ≤50 ml/min.The overall burden of CRI associated anemia,defined as hemoglobin <11 g/dl, was 800,000 adults.The public health burden of anemia associated with CRI may be substantial, given the large number of people with CRI; and that even a modest reduction in renal function is associated with decreased hemoglobin level.