Coarctectomy in 190 children aged over 1 year to 15 years at operation produced a significant reduction in blood pressure for the group as a whole. Forty-nine patients (24 percent) remained hypertensive. Postoperative hypertension was unexplained in 29 (15 percent) of the 190 patients, and coarctation persisted or recurred in 20 (11 percent). For patients operated on between the ages of 4 and 15 years the earlier the age of operation, the greater the reduction in the blood pressure index: (measured blood pressure/normal mean systolic [or diastolic] blood pressure for age) X 100.