We describe three children with chronic renal failure who developed mitral obstructive disease over a period when maintained on hemodialysis. The development and progression of the mitral disease was documented by cardiac catheterization in one child and by Doppler echocardiography in the other two children. These three patients had the lowest body weight among the 16 children undergoing chronic dialysis who were examined cardiologically in our hospital. Autopsy in one child who died from heart failure revealed marked thickening of the leaflets and subvalvar apparatus of the mitral valve with severe obliteration of the intercordal spaces. We found no sign of calcification at the mitral annulus nor at the attachments of the leaflets of the aortic valve, and no Ashoff bodies. We attempted percutaneous catheter balloon valvoplasty in one child which permitted successful renal transplantation after failure of an initial transplantation because of severe pulmonary venous congestion. We conclude that mitral obstructive disease could be a complication of long-term hemodialysis for chronic renal failure. Catheter intervention may serve to release the obstruction, although the procedure is not curative.