Earlier studies have shown that the aortic root, in analogy with the mitral annulus, moves towards the left ventricular apex during systole. However, there are no earlier studies comparing the amplitude of the aortic annulus motion (AAM) with that of the mitral annulus (MAM), which was the main aim of the study. Another aim was to study the intra- and interobserver reproducibility (IIOR) of measuring AAM with M-mode and 2-D echocardiography as it is not obvious which of the methods that should be used. Twenty-one healthy subjects were examined by echocardiography. AAM and MAM were measured at different sites. IIOR was measured in 10 of the subjects. There was no significant difference between average AAM (15.3 +/- 1.5 mm) and average MAM (15.6 +/- 1.5 mm) and there was a rather good agreement between the variables. There was also no significant difference between AAM at the septal site (16.3 +/- 2 mm) and average MAM, but a significant difference between AAM at the lateral site (14.2 +/- 1.6 mm) and average MAM (P<0.001) and between the both sites of measuring AAM (P<0.001). The significant difference between the two sites of measuring AAM may have anatomical reasons but may also depend on difficulties in measuring AAM at the septal site where it has lower reproducibility than at the lateral site. IIOR of measuring AAM was good when using M-mode but poor when using 2-D echocardiography and AAM should preferably be measured using M-mode and not using 2-D echocardiography.