A three year old girl with severe congenital mitral stenosis was successfully treated by percutaneous balloon dilatation of the mitral valve. Cardiac catheterisation and cross sectional and Doppler echocardiography indicated that the orifice of the mitral valve had doubled in area. A small atrial septal defect was found at follow up cardiac catheterisation and angiography. Balloon dilatation of the mitral valve is a reasonable alternative to surgical treatment for typical congenital mitral stenosis even in young children.