Pulmonary valve stenosis was relieved by balloon dilatation during cardiac catheterisation on 27 occasions in 23 infants and children aged 7 days to 12 years, median 31 months (three aged less than 2 weeks). Pulmonary valve diameter was estimated by cross sectional echocardiography to assist in the choice of balloon size. Before dilatation the right ventricular systolic pressure ranged from 41 to 190 (median 92) mm Hg and was suprasystemic in 10 patients. There were significant reductions in the ratio of right ventricular to systemic systolic pressure and pulmonary systolic pressure gradients immediately after balloon dilatation. Twelve patients underwent recatheterisation (11 at six months and one at one week after balloon dilatation), which showed further improvement with significant reductions in right ventricular pressure or pulmonary valve gradient or both, particularly in the patients with the least satisfactory initial results. This improvement was attributed to resolution of the obstruction at infundibular level. Repeat pulmonary valve dilatation was successfully performed in four patients who had poor results after initial dilatation. Balloon pulmonary valvotomy appears to provide good short term and medium term relief of pulmonary valve stenosis and may obviate the need for surgery in many cases. An apparently poor immediate haemodynamic result does not preclude a good longer term result.