Las Higueras Talcahuano. Chile.Atherosclerosis (AS) is a progressive illness with onset in childhood, and the main cause of death in Western civilization. AS earliest lesions are usually seen in children under one year of age and small children, manifesting as a lesion called fat grooves. Aim: To find and characterize anatomically and pathologically AS lesions in fetuses and newborns. Methods: We studied 13 aortas obtained from autopsies; each aorta was opened lengthwise and examined macroscopically, fixed in 10% formaline and stained with hematoxylin and VanGieson. They were then examined microscopically. Some sections with lesions were fixed in 3% glutaraldehyde for scanning or transmission electronic microscopy. Macroscopic studies: number of lesions, localization, size, color, prominence or not and degree of delimitation. Microscopic studies: type and ultrastructural characterization of AS lesions. Results: Six out of 13 aortas presented lesions (46%); 9 were gray lesions, 100% were well-defined, 9 lesions were not elevated; 91% measured less than 4 mm. The most frequent localization was in abdominal aorta (64%). The great majority of the opposing lesions corresponded to fat groove, some were incipient fibrous plaque. These lesions did not differ from those described in adults either in conventional microscopy or ultrastructure. Conclusion: It is worthwhile mentioning the large amount of AS lesions in the studied aortas. We believe that AS lesions could be a non-pathological process present in arteries of medium and great caliber in human beings at early stages in life. Results: Of the total results, 97.9 % were S, and 94% of these x AP. According to the study type, 28.3% were A, 0,27% B, and 67% AB. 55% of the neonates were male. There were 1.6 lesions by patient; 30% had DA, 21% A, 18% LBW, 18% UI, 4% SI, 3% T, 1% IH, and 5% O. Asphyxia predominated among infants older than 37 gestational weeks and above 2500 g; 52% was secondary to lung disease. DA were more frequent among infants older than 29 gestational weeks, with a birth weight above 1000 g, and who died during the first hour of life. UI were more frequent at the highest and lowest gestational ages and birth weights, and from the first postnatal week on; 82% of UI involved the respiratory system. The most frequent SI were candidiasis and streptococcal infections. Hyaline Membrane Disease and Intraventricular Hemorrhage were more frequent in LBW. 67% of T were bronchopulmonary dysplasias. Conclusions: Autopsy is a reliable method to detect lesions associated with neonatal death, as well as a useful tool for assistance surveillance. Study types: A: autopsy and placental examination; B: external examination of the fetus and placenta; AB: only autopsy. According to birth weight, the patients were classified as Յ 1000g, 1001 -1500 g, 1501 -2500 g, and Ն 2501 g; according to gestational age (GA), as Յ 19 weeks (w), 20 -27 w, 28 -36 w, and Ն 36 w. Results: Of the total results, 95.6 % were S, and 94.8 % of these were S x AP. 87.2% were study type A, 4.7 % t...