Digitised left ventricular echocardiograms were studied in nine children with congenital mitral stenosis to assess the severity of inflow obstruction. In six children the two prime indices of mitral stenosis were abnormal, with a prolonged time from minimum dimension to 20 per cent dimension change and a reduced peak dimension change during diastole. In three, however, these values did not suggest inflow obstruction, depsite significant gradients at cardiac catheterisation. Two-dimensional echocardiography was performed in 10 children with congenital mitral stenosis to determine the mitral annular size and the morphology of the valve and subvalvular apparatus. The annular size and number of papillary muscles could be assessed along with the detection of combined mitral abnormalities. Two-dimensional studies can reliably delineate the type of mitral abnormality, and should be performed in all cases with congenital heart disease having a high incidence of associated left ventricular inflow obstruction. Digitised M-mode left ventricular echocardiography is in general unreliable in assessing congenital obstruction, though it may be of some value in individual cases.