Background: Mitral annulus (MA) area is derived during transthoracic echocardiography (TTE) assuming of a circu‑ lar shape using the MA diameter from the apical 4 chamber (A4c) view. Since the MA is not a circular structure, we hypothesized that an elliptical model using parasternal long-axis (PLAX) and apical 2 chamber (A2c) view measured MA diameters would have better agreement with 3-dimensional transesophageal echocardiography (3D TEE) meas‑ ured MA in degenerative mitral valve disease (DMVD). Methods: Seventy-six patients with moderate-to-severe DMVD had 2D TTE and 3D TEE performed. MA area was measured retrospectively using semi-automatic modeling of 3D data (3D ­TEEsa ) and considered as the reference method. MA diameters were measured using different 2D TTE views. MA area was calculated using assumptions of a circular or an elliptical shape. 2D TTE derived and 3D ­TEEsa . MA areas were compared using linear regression and Bland-Altman analysis. Results: The median MA area measured at 3D ­TEEsa was 1,386 (1,293–1,673) ­mm2 . With 2D TTE, the circular model using A4c view diameter resulted in a small systematic underestimation of MA area (6%), while the elliptical model using PLAX and A2c diameters resulted in 25% systematic underestimation. The standard deviations of the distribu‑tions of inter-method differences were wide for all 2D TTE methods (265–289 ­mm2 ) when compared to 3D ­TEEsa , indicating imprecision. Conclusions When compared with 3D ­TEEsa modeling of the MA as the reference, the assumption of a circular shapeusing A4c TTE view diameter was the method with the least systematic error to assess MA area in DMVD and moder‑ ate to severe regurgitation.