The size of the aortic arch and thoracic aorta was measured in 50 healthy volunteers studied by NMR. In each case the following parameters were measured and statistically elaborated: diameter (in mm) of ascending aorta (between onset and arch beginning), of aortic arch (intermediate zone), of isthmus, of descending aorta (between isthmus and diaphragm), of diaphragmatic isthmus; a mean diameter was also calculated, and for every diameter mean and standard deviation were obtained. Moreover, the length (in mm) of superior and inferior contours of the aortic arch, as the ratio of these two values were obtained. At last, total length of considered aortic tract, area of visualized surface and theoretic volume were obtained. For each parameter a diagram was then plotted, with age in ordinates and values of above mentioned parameters in abscissae. Statistical evaluation allows to affirm that the size of the aorta grows with ageing. On the contrary, the ratio between superior and inferior contour of the aortic arch tends to remain unvaried; this fact seems to disagree with the current opinion that the superior wall of the arch grows with age more than the inferior one.