Recent evidence strongly suggests that peroxidative modification of lipids may play a significant role in atherogenesis. In our present research, we investigated if the oxidative stress mediated by oxygen free radicals was a pathophysiologic condition that occurred in the early stages of human development. Thus the aim of this research was to examine lipid peroxidation in human fetal aortas. Human fetal aortas and proximal iliac arteries (n= 8) were obtained from fetuses aged 7 ± 2 months, immediately after autopsy. Lipids from the initial fatty streak lesions (LFS) and the vessels uninvolved (LUV) were extracted by the chloroform/methanol method. Lipid peroxidation levels were measured by two different methods: determination of lipid conjugate dienes (the spectrum trend was recorded from 320 to 200 nm with a spectrophotometer) and malonyldialdehyde (MDA) content (TBA method). We observed that lipid conjugated dienes were present in LFS, but not in LUV, with a characteristic absorption peak at 233 nm. In addition, MDA levels were significantly higher when the LFS = 3.85 ± 0.91 nmol than when the LUV = O.41 ± 0.12 nmol (p<0.001 versus LUV). The presence of lipid peroxidation in our samples could be mediated by free radical production in the first stages of human development. Thus these data suggest that LFS peroxidation mediated by free radicals occurs in the vascular circulation in the early stages of human development. This could influence the progression of vascular damage and atherosclerotic disea