Introduction: Left atrial (LA) size is an indicator of the pressure to which it is chronically subjected. Although guidelines recommend measuring it using volume indexed to body surface, the anteroposterior diameter is still normally used. Aim: To evaluate which of these measurements correlates better with atrial pressure-related echocardiographic parameters. Methods: Atrial diameter and volume, together with parameters of systolic function, diastolic function, pressure, and degree of mitral regurgitation, were measured in 121 consecutive outpatients. Results: Atrial diameter correlated with its indexed volume (r: 0.69) with a low degree of agreement for detecting dilation (Kappa: 0.51). Atrial diameter was related to the parameters associated with atrial pressure: E/E′ (r: 0.44), pulmonary vein systolic/diastolic rates quotient (r: 0.25) and degree of mitral regurgitation (r: 0.19). The correlations improved when volume indexed to body surface was measured (r: 0.52; 0.38 and 0.44, respectively). In a multiple regression analysis that included E/E′, pulmonary vein flow and degree of mitral regurgitation, LA diameter depended entirely on E/E′ (r: 0.44; B: 0.04; P: 0.000). The relationship improved when the diameter was corrected for body surface or the volume was measured (r: 0.54 and 0.54, respectively), and in particular when volume indexed to body surface was measured (r: 0.66). In this case, pulmonary vein flow (B: 6.8; P: 0.03), degree of mitral regurgitation (B: 5.2; P: 0.000) and E/E′ ratio (B: 0.8; P : 0.000) were included in the equation. Conclusions: Indexed atrial volume correlates better with LA pressure surrogates than the anteroposterior diameter, even when this is corrected for body surface. (Echocardiography 2010;27:1049-1055)