Background: DXA directly measures Whole Body (WB) Bone Mineral Content (BMC)and Fat Mass (FM); it can be useful for nutritional assessment in neonates. When using Hologic densitometer, two software are available for neonates: Pediatric WB(PWB)and Infant WB (IWB)which is used with infant table pad. Aim of study: comparison between PWB and IWB for BC assessment in small subjects. Methods: Seven newborn piglets (1430 to 5180g) were killed and underwent triplicate DXA with PWB and then with IWB; in 4 piglets Fat Content (FC) was increased with porcine lard added around the abdomen.After complete homogenization whole carcass chemical analysis,total FC(gravimetric method after fat extraction) and total calcium content (Ca)(atomic absorptiometry). Reproducibility (CV) of PWB and IWB was compared using paired t-test and accuracy was assessed as presiously described (Picaud Am J Clin Nutr 1996; 63: 157-63). Results: CV was significantly different for BMC (PWB: 4.2±2.6 percent, IWB: 2.5±1.0 percent, p=0.044), but was similar for FM (PWB: 5.5± 3.3 percent, IWB: 6.6±3.1 percent, p=0.180). DXA estimates of BMC and FM were significantly correlated with Ca and FC; correlation coefficient was better for IWB (BMC: r=0.987, FM: r=0.980) than for PWB (BMC:r=0.925, FM:0.962).Mean DXA measurement error (percent) for PWB and IWB differed significantly for BMC(PWB:: 19 percent, IWB: 9 percent) but were similar for FM (PWB: 41.1 percent, IWB: 42.2 percent). Conclusion: Caution is needeed when using DXA in small subjects: BMC assessment with IWB was better than with PWB and FM assessment needs to be improved for the two software.