Several surgical techniques have been proposed for obstructive hypertrophic cardiomyopathy (OHCM): myotomy, mitral valve replacement (MVR), or myotomy-myomectomy (MM). We reviewed our series of 47 patients who had undergone surgery in order to determine their prognosis and to know whether MVR+MM was better than MM only. Left intraventricular gradient decreased from 86 +/- 34 mmHg to 15 +/- 20 mmHg (P < 0.0001). Postoperatively, three patients died from low cardiac output (6.4%); five died later. Annual mortality (including postoperative deaths) was 3.0%. Follow-up was 5.7 +/- 0.7 years. Survival was 87 +/- 11% at 12 years. After operation, 91% had NYHA class I or II dyspnoea (before surgery this had been 28%); chest pain was CCS class I in 88% (vs 47%); 12% had had syncope since operation (vs 53%). The gradient decrease was larger in the MM+MVR group (P < 0.05). Survival and functional improvement were similar in the two groups. Mitral regurgitation decreased from 2.7 to 0 in the MM+MVR group (P < 0.0001), whereas it decreased from 1.5 to 1.2 in the MM group (ns). MM appears to be the procedure of choice. When mitral regurgitation is important or when an intrinsic disease of the mitral valve exists, the addition of MVR should be considered.