The objective of this study was to assess the validity of multidimensional transoesophageal echocardiography (TOE) in the determination of the orificial surface area of aortic stenosis (AS) in 85 patients, using as a reference the surface area calculated on transthoracic ultrasonography (TTU) by applying the continuity principle (n = 75) and/or by haemodynamic studies using Gorlin's formula (n = 40). Planimetry was able to be performed in 78 of the 85 patients (92%). Planimetry was impossible in 7 patients with massive calcification of the aortic orifice (n = 5) or posterior valve (n = 2). The mean value of the selected angle was 45 +/- 13 degrees (0 to 78 degrees). An excellent correlation was observed between aortic surface area (ASA) measured by multidimensional TOE and TTU (r = 0.94; y = 0.90x +/- 0.10; SEE = 0.10 cm2; p < 0.001). Similarly, the ASA on multidimensional TOE was also well correlated with the haemodynamic surface area (r = 0.90, y = 0.94x +/- 0.05; SEE = 0.09 cm2; p < 0.001). The correlations between multidimensional TOE and TTU measurements (n = 26; r = 0.96; y = 0.85 x +/- 0.11; SEE = 0.07 cm2; p < 0.001) and cardiac catheterization (n = 13; r = 0.92; y = 0.77 x +/- 0.7; SEE = 0.09 cm2; p < 0.001) remained satisfactory in patients with associated aortic incompetence. Multidimensional TOE identifies cases of AS with an ASA on TOE or haemodynamic studies less than or equal to 0.75 cm2 with sensitivities of 93% and 92%, respectively, and a specificity of 100%. Overall, multidimensional TOE allows a precise and reliable evaluation of ASA in the great majority of cases of AS.