Aims: Whereas transthoracic echocardiography is the modality of choice for the diagnosis of severe aortic stenosis and cine-fluoroscopy is used to guide the implantation of the TAVI prosthesis, we believe that multislice computer tomography (MSCT) is the modality of choice for evaluation of the aortic root with a view to selecting patients with suitable anatomy and to guide sizing. We aim to describe an anatomical approach for the step by step interrogation of a 3D MSCT dataset to obtain the measurements of the aortic root required for patient selection, sizing and selection of the optimal angulation of the C-arm during the implantation procedure. Methods and results: The landmarks used to anatomically define the aortic annulus and structures of the aortic root may be used to define the same structures for measurement on a 3D MSCT dataset by setting up orthogonal cut-planes including one axial to the aortic annulus. This allows true axial diameter measurements and also enables us to define the valve plane. Conclusions: Measurement on the axial images avoids incorrect diameter measurements that do not pass through the central axis.