The diameter of the aortic root was measured in 151 patients with small ventricular septal defect (Qp/Qs less than 2 and pulmonary vascular resistance less than 1.5 U.m-2) and correlated with the presence of absence of aortic regurgitation. In 26 cases the aortic juxtavalvular region (bulbus) was dilated above 2 SD compared to a control group. All patients with aortic regurgitation of with cusp prolapse belonged to this group of 26 cases. Aortic root dilatation seems to have a specificity of 89 p. 100, a sensitivity of 75 p. 100 and a negative predictive value of 98 p. 100 in relation to the occurrence of aortic insufficiency. The finding of an aortic root dilatation associated with a ventricular septal defect should incite to a closer supervision of non-operated patients should be used as an argument when discussing the surgical closure of the ventricular septal defect.