Tricuspid stenosis was identified clinically and confirmed by cardiac catheterization in twelve patients. In one patient the lesion was isolated. It was associated with mitral disease in four, and with both aortic and mitral lesions in seven. Two patients came to autopsy and two underwent tricuspid valvuloplasty. The most striking clinical feature was a characteristic diastolic murmur with a thrill in the third, fourth and fifth intercostal spaces to the left of the sternum. The increase in intensity of the murmur during inspiration and the decrease during expiration aided greatly in identifying the murmur and differentiating it from that of mitral stenosis. The intensity of the murmur varied with respiration in the same manner as the transvalvular diastolic pressure gradient. An opening snap of the tricuspid valve was heard in only three cases. Dyspnea, fatigue and edema were the most common symptoms but the resulting disability was quite variable. Recurrent ascites was present in three patients. The right atrium was enlarged in every patient but was massive in only three. The largest right atria, the most severe right atrial hypertension and the greatest tendency to develop edema were associated with coexisting tricuspid insufficiency, multivalvular disease and atrial fibrillation. Tall P waves, often taller than QRS in V1, and low QRS complexes with an rsr′ pattern in lead V1 were common features of the electrocardiogram. In one patient the area of the tricuspid orifice estimated from data obtained at cardiac catheterization and that determined by planimetery of a postmortem photograph of the valve were identical. In two patients in whom autopsy was performed the tricuspid valve was less stenotic and deformed than the mitral valve. The pulmonary vascular pressures and resistance in patients with mitral and tricuspid stenosis were lower than in patients with a similar degree of mitral stenosis alone. Pulmonary venous hypertension, however, was not entirely prevented and most of the patients had pulmonary congestive symptoms of mitral stenosis, including orthopnea. The failure of one patient to improve following mitral valvuloplasty was attributed to the tricuspid stenosis.