We retrospectively reviewed the 26-year National Institutes of Health experience with operative treatment of obstructive hypertrophic cardiomyopathy in pediatric patients. Operative criteria were either severe obstructive symptoms (New York Heart Association functional class III or IV) or sudden death. Seventeen patients underwent 19 open procedures, of which the present study is comprised. Complete follow-up was available 10.1 +/- 1.4 years (mean +/- standard error; range, 0.8 to 26.2 years) after operation. The mean ages at diagnosis and operation were 11.9 +/- 1.3 years (range, 1 to 17 years) and 14.8 +/- 0.7 years (range, 9 to 17 years), respectively. The preoperative intraventricular septum mean dimension was 23.2 +/- 1.3 mm (range, 11 to 36 mm). The left ventricular outflow tract gradient was 74 +/- 9 mm Hg (range, 20 to 175 mm Hg) at rest and 94 +/- 7 mm Hg (range, 55 to 175 mm Hg) with provocation. Fifteen patients (88%) underwent left ventricular myotomy and myectomy, and 2 underwent mitral valve replacement. Two patients who initially received left ventricular myotomy and myectomy later underwent mitral valve replacement. There were one perioperative death (6%) and five late sudden deaths (31%) at 3.8, 8.7, 9.6, 14.1, and 21 years postoperatively. Kaplan-Meier survival was 86% +/- 8% at 5 years and 77% +/- 12% at 10 years. After operation, the left ventricular outflow tract gradient decreased almost 80% to 21 +/- 15 mm Hg (p = 0.0001). In 8 patients, the left ventricular outflow tract gradient completely resolved.(ABSTRACT TRUNCATED AT 250 WORDS)