Twelve patients, three male and nine female, suffering from hypertrophic obstructive cardiomyopathy were operated during the period 1976 to 1991. Operative methods were myotomy-myectomy (Morrow-procedure), mitral valve implantation or both. During the perioperative period two patients developed conduction disturbances requiring pacemaker implantation, five patients had left bundle branch block, and one died. The NYHA class was significantly reduced postoperatively (p = 0.0002). Five of eleven patients surviving the perioperative period died postoperatively after a mean follow-up of 6.3 years. It is the authors' opinion, that operation should be considered in patients suffering from hypertrophic obstructive cardiomyopathy, who have a left ventricle outflow gradient of 50 mmHg or more, and who despite medical treatment have symptoms placing them in NYHA class III-IV.