The aim of this study is to specify the feasibility and value of the diameter measurement of the jet of aortic insufficiency (AI) in colour Doppler. 68 consecutive patients had a supra-sigmoid angiography and a colour echo-Doppler. An aortic insufficiency was revealed 58 times by the angiography and Doppler. In all the cases except four, it has been possible to measure the jet diameter at the origin in para-sternal incidence in colour TM by confronting the images in great and small axis section. The Doppler results have been compared to the angiographic score in 4 grades according to Sellers classification. The jet diameter at the origin in colour TM is significantly different in groups I, II, III-IV. In the group III-IV, it is always higher or equal to 13 mm. The failures of quantification of the AI jet in colour Doppler are linked with the very eccentric nature of the jet or to the poor quality of the echo-Doppler imaging. On the whole, the jet diameter measurement proves to be a very useful element in the assessment of the gravity of an AI, particularly when it is a central and circular jet.