Seven patients with isolated congenital mitral stenosis are described. In one instance there was an associated coarctation of the aorta. Repeated pulmonic infections, pulmonary edema, and congestive heart failure occurred frequently. The clinical diagnosis is suspected in the presence of an apical diastolic rumbling murmur and left atrial enlargement. Presystolic accentuation of this diastolic murmur, a sharp first heart sound, and an opening snap strengthen the diagnosis. Cardiomegaly and the electrocardiographic finding of right ventricular hypertrophy are common. Pulmonary hypertension and congestive heart failure may obscure the clinical picture of isolated congenital mitral stenosis. In infancy, the presence of tight mitral stenosis is usually associated with a poor prognosis. The mitral leaflets showed variable degrees of fusion and thickening. The chordae tendineae were shortened and the papillary muscles hypertrophic. Endocardial fibroelastosis was common in the left heart, especially in the atrium. In infancy and early childhood, the results of the medical and surgical treatment were generally poor. In older children, a better result was obtained and the surgical indications in these instances are not unlike those of rheumatic mitral stenosis.