Transcatheter aortic valve implantation (TAVI) is a valuable alternative for aortic valve replacement in selected high-risk candidates. Accurate preoperative assessment of the aortic annular dimensions is crucial for the success of TAVI, since choice of an incorrectly sized prosthesis may result in catastrophic complications. These complications include annular rupture and coronary arterial obstruction, if the prosthesis is too big, or prosthesis migration and severe paravalvular leakage, if the prosthesis is too small. According to current recommendations, the choice of prosthesis size is based on transoesophageal echocardiography (TEE) measurements. However, TEE results are dependent on operator experience. Moreover, recent research has shown that TEE can significantly underestimate annular dimensional measurements. Alternative sizing methods based on Multidetector Computed Tomography (MDCT) or manometry during balloon aortic valvuloplasty have therefore been developed. We present a brief overview of the imaging modalities available for preoperative assessment of annular size and discuss their potential advantages and limitations.