We have reviewed the results of two different forms of surgical management of hypertrophic obstructive cardiomyopathy refractory to medical therapy. Twenty-one patients were treated with 22 procedures between 1963 and 1987. Eleven underwent a ventricular septal procedure by myotomy with or without myectomy, and 11 underwent mitral valve replacement (MVR), 1 of whom had previously undergone a ventricular septal procedure. The groups were comparable with respect to severity and duration of symptoms, age range, electrocardiographic features, and hemodynamic changes. Mitral valve replacement produced a greater and more consistent reduction in the left ventricular outflow tract pressure gradient than a ventricular septal procedure (MVR, 68.3 mm Hg preoperatively and 2.5 mm Hg postoperatively; ventricular septal procedure, 60.1 mm Hg preoperatively and 13.4 mm Hg postoperatively). This was associated with better postoperative ventricular configuration in diastole and more apparent loss of midcavity narrowing in systole. Ejection fraction did not fall after a ventricular septal procedure but decreased significantly from a mean of 79% to a mean of 61% after MVR. Similarly, left ventricular end-diastolic pressure remained unchanged after a ventricular septal procedure but fell from a mean of 26.6 mm Hg to 17 mm Hg after MVR. Although both groups experienced a generally satisfactory symptomatic result, this appeared more reliable with MVR. We suggest that MVR offers a more predictable improvement than a ventricular septal procedure and may be the procedure of choice for units with limited experience with ventricular septal procedures.