Echocardiographic analysis of the movement of the posterior mitral valve leaflet in 60 patients with lone mitral stenosis, 35 patients with aortic stenosis, and 18 patients with aortic and mitral stenosis showed a spectrum of initial posterior mitral valve leaflet movement in early diastole. The classical anterior movement was seen in 36 out of 60 patients with mitral stenosis (60%), and 8 out of 16 patients with aortic and mitral stenosis (50%). Normal posterior movement was present in all patients with lone aortic stenosis but was also seen in 10 patients (17%) with mitral stenosis and 6 patients (33%) with aortic and mitral stenosis. The remaining patients with mitral stenosis or aortic stenosis and mitral stenosis showed a biphasic type of initial movement. Patients with anterior movement had a mean calculated mitral valve area from cardiac catheterisation significantly smaller than the rest (P less than 0.001), but neither biphasic nor posterior movement excluded severe mitral stenosis. The distinction between patients with mitral stenosis and initial movement of the posterior mitral valve leaflet and patients with left ventricular discompliance is possible when there is sinus rhythm. Late diastolic anterior movement of the posterior mitral valve leaflet during atrial contraction is diagnostic of true mitral stenosis.