The aim of this study was to assess body composition in children with chronic renal failure (CRF) and post renal transplantation (Tx), and to compare it to body mass index (BMI) and nutritional intake. Dietary assessment using 3-day diaries, total and regional body composition assessment by dual x-ray energy absorptiometry of 50 CRF children (29M, 21F), median age 8.9 yrs and 50 Tx children (32M, 18F), median age 12.9 yrs. BMI, percentage fat mass (%FM) and lean mass (LM) were corrected for height and expressed as SDS (HSDS). In both groups, BMIHSDS was lower than %FMHSDS and higher than LMHSDS (p<0.05). In the Tx group, there were associations on bivariate analysis between energy & protein intake and BMIHSDS & %FMHSDS (r,0.5, p<0.05), and between LMHSDS and protein intake (r,0.5, p<0.05). On multivariate analysis, there was an association between LMHSDS and time since transplantation (r,-0.4, p<0.05). Children in the CRF and Tx groups had a high percentage predicted trunk:leg FM ratio of 148% and 157%, respectively. Children with CRF and Tx have discordant body composition with a relatively high FM and low LM, which is not reflected by BMI. In addition, they appear to have an increased level of central adiposity that may predispose them to increased morbidity in later life.