Accurate measurements of LBM are needed to study the effect of highly active antiretroviral therapy (HAART) upon growth in HIV-infected children. To determine the accuracy of newer procedures including BIA (using recently published modified equations) to the traditional method of anthropometrics(ANTHRO) in measuring LBM, values calculated by these methods were compared in a cohort of HIV infected children. Twenty prepubertal children ages 1.4 to 13.2 years with congenital HIV infection and heterogeneous growth patterns (11 with normal growth, 4 failing to thrive, 3 with wasting syndrome, and 2 with stunted growth) underwent LBM measurements by BIA and ANTHRO (skinfold measurements using Lang's caliper at the triceps, biceps, subscapular, and suprailiac sites). In 10 of 20 children, ages 7-13, 2 additional methods for LBM assessment (DEXA: dual energy x-ray absorptiometry and D-H2O:doubly-lableled water technique) were also applied. LBM values for each patient were compared between different methods by regression analysis. The correlation between LBM (kg) by BIA and by ANTHRO was significant (n=20, r=.98, P<.0001). The mean±standard deviation values for LBM in 10 older children by ANTHRO was 22.7±2.7, by BIA was 22.7±3.1, by D-H2O was 22.6±3.7, and by DEXA was 21.4±3.4. The comparison of the 4 different methods by regression analysis were ANTHRO v D-H2O: r=.88, p<.01, ANTHRO v DEXA:r=.90, P<.001, ANTHRO v BIA: r=.92, p<.001, BIA v DEXA: r=.92, p<.001, and BIA v DH2O: r=.93, p<.001.Conclusions The comparison of currently available methods for LBM measurements to LBM as assessed by ANTHRO suggest that these methods can be used to acBIA assessment using modified equations for LBM correlated well with ANTHRO data even in very young children and this correlation was linear up to the early teen years. Since BIA is a quick procedure that is easy to use, this study further suggests that the BIA tool can and should be applied in assessing the impact of HAART in HIV-infected children.