Fifty balloon angioplasties of branch pulmonary artery stenosis in 34 patients aged 4 months to 20 years, performed in 7 French Centres, were included in this study: they were performed from 1984 to 1991 and concerned severe stenoses which were congenital in 36 cases and secondary to surgery in 14 cases. The criteria of inclusion were: diameter of stenosis less than or equal to 8 mm, right ventricular systolic pressure (RVP) greater than or equal to 50 mmHg, RVP/aortic pressure ratio (RVP/AO) greater than or equal to 50%, and a significant perfusion defect on radionuclide angioscintigraphy. There were no operative complications. The diameter of the stenosis increased by greater than 40% in 23 cases (46%); in only 7 of these cases (14%) did the RVP and RVP/AO ratio decrease by more than 20%, the RVP being less than 50 mmHg, or did the perfusion scintigraphy improve. No cases of restenosis were observed. The reasons for failure are discussed together with the limitations of this study. The respective indications of surgery and angioplasty are not easy to determine for these complicated lesions. New techniques such as the use of stents should improve results.