In 64 consecutive subjects (age range 17-69 years) we compared the antero-posterior (A-P) size of the left atrium estimated by M-mode and wide-angle two-dimensional echocardiography (short and long axis parasternal views). M-mode A-P diameter correlated both with short (r = 0.82) and with long (r = 0.76) axis A-P diameter. Subsequently we quantitatively analysed by two-dimensional echocardiography A-P, cranio-caudal (C-C) and latero-lateral (L-L) left atrial dimensions in 20 patients with mitral valve disease (age range 24-66 years) and in 24 normal subjects of comparable age range. Subjects with mitral valve disease had significantly higher A-P (P less than 0.001), C-C (P less than 0.02) and L-L (P less than 0.001) left atrial dimensions than normal controls. Both in normals and in mitral valve disease patients C-C was the view that showed the largest atrial diameter. Left atrial shape was however more spherical in mitral valve patients. Of these 7/20 (35%) had abnormal A-P diameter compared to the normal subjects. Patients with abnormal L-L and C-C left atrial dimensions were 9/20 (45%) and 7/20 (35%). Five of the patients with increased L-L size had a normal A-P diameter. Our results demonstrate the usefulness of wide-angle two-dimensional echocardiography in the assessment of the left atrial enlargement, especially in patients with negative or borderline M-mode echocardiographic data.