Balloon angioplasty for branch pulmonary artery stenosis was reported from 27 institutions to the Valvuloplasty and Angioplasty of Congenital Anomalies Registry. One hundred eighty-two procedures were performed in 156 patients ranging in age from 0.2 to 46.2 years (mean 7.7). Short-term angiographic appearance, hemodynamic results and immediate complications were recorded. Vessel dimension at the site of stenosis increased from 4.5 +/- 2.0 (mean +/- standard deviation) to 6.8 +/- 3.0 mm (p less than 0.001) with greater increases in vessel dimension at the site of stenosis if the balloon diameter was greater than 3 X the original dimension of the stenosis. There was no significant benefit related to age or prior surgical intervention. The mean peak systolic pressure gradient was reduced from 49 +/- 25 to 37 +/- 26 mm Hg (p less than 0.001) and pressure proximal to the stenosis decreased from 69 +/- 25 to 63 +/- 24 mm Hg (p less than 0.001). Complications occurred in 21 patients and included vessel rupture and death in 2 patients, vessel perforation or rupture with survival in 3, cardiac arrest and death in 1, paradoxical embolism and death in 1 and low output and death in 1. Balloon angioplasty for branch pulmonary artery stenosis increases vessel dimension at the site of stenosis, reduces systolic pressure gradient and to a minor degree, reduces proximal pressure. Long-term outcome and potential complications are as yet uncertain.