Mitral valve area (MVA) in 30 patients with mitral stenosis (MS) and 34 normal controls was calculated by real-time, 3-dimensional echocardiography (RT3DE); MVA in patients with MS correlated well with the mitral area determined by 2-dimensional echocardiography (r = 0.98) and by pressure half-time (r = 0.90). MVA in normal controls on RT3DE correlated well with MVA on 2-dimensional echocardiography (r = 0.94) and pressure half-time (r = 0.91). There were significant differences between the orifice areas in patients with MS and normal controls. RT3DE can provide not only the anatomic structure of mitral valve apparatus, but also the optimal plane of the smallest mitral valve orifice, and can thus accurately measure the MVA.