Growth retardation and malnutrition are pervasive complications of childhood chronic renal insufficiency (CRI). Many of the losses in growth and nutritional status occur before initiation of renal replacement therapy (RRT) with dialysis or kidney transplantation. Studies in adults have established that declining renal function results in progressive malnutrition with a consequent increased risk of complications and death. The influence of declining renal function on growth and nutrition in children has not been characterized. The unique needs of growing children may result in the presence of malnutrition and growth retardation at a level of renal function well above that identified as a risk for malnutrition in adults. Several methods of estimating renal function exist. Accurate identification of children at risk for malnutrition requires that the measure of renal function, which best reflects nutritional status be determined. The goals of this study are: (I) To determine the impact of declining renal function on growth and nutrition, (II) to identify independent risk factors for progressive malnutrition and growth failure, and (III) To compare four methods of estimating renal function and to determine which best reflects nutritional status. This cross-sectional study will use a 4-component model of body composition, as well as dual energy X-ray absorptiometry and anthropometric methods, to evaluate nutritional status and growth. The impact of declining renal function on these parameters will be assessed by univariate linear regression. The regression model will be expanded to identify risk factors for impaired growth and nutrition. Logistic regression and ROC analysis will be used to provide a quantitative comparison of each renal function measure's ability to discriminate between patients with and without malnutrition.