Introduction. The anatomy and role of the aorta in prenatal life differ from those in postnatal life. Aim. We aimed at investigating the development of the aorta during a period between the 4th and 8th months of fetal life. We also analyzed the influence of sex on the values of the parameters examined. Materials and methods. We examined the diameters of aortas in 223 human fetuses, including 108 males and 115 females, aged between 4 and 8 months of prenatal life. The entire material was obtained from the Department of Histology and Embryology at the Collegium Medicum, Nicolaus Copernicus University in Bydgoszcz, Poland. All fetal specimens had been conserved in a 9% formaldehyde solution for a period of more than 3 months. Only spontaneously aborted fetuses of a normal morphology and a normal karyotype were used in this research. We measured the diameter of the proximal and distal ascending aorta, of the aortic arch, and of the proximal thoracic aorta. The measurements were taken in the following locations: the diameter of the proximal ascending aorta was taken at the level of the aortic valve; the diameter of the distal ascending aorta was taken at the ostium of the brachiocephalic trunk; the diameter of the aortic arch was taken between the ostium of the left common carotid artery and the left subclavian artery; the diameter of the proximal thoracic aorta was measured just beneath the arterial duct. Results, Discussion and Conclusions. All analyzed diameters grew linearly in time. We found no significant differences in the anatomy of the aorta with respect to sex. The ascending aorta is broader than the descending, thoracic aorta.