The authors describe the technique of percutaneous balloon mitral valvuloplasty and the results in the first 12 patients treated in Norway. One patient experienced a serious complication, but has later been treated successfully. The average maximal gradient and mean gradient were reduced from 21 mm Hg to 8 mm Hg and from 12 mm Hg to 4 mm Hg respectively. The average size of the valve orifice increased from 1.0 cm2 to 2.2 cm2. Echo-cardiographic follow-up after one year revealed no restenoses. The indications and contraindications are discussed.