Palliation of children with large ventricular septal defects (VSD) by pulmonary artery banding (PAB) is associated with a variety of unfavorable sequelae. We document another possible complication of PAB, the development of subaortic stenosis, which occurred in 4 of 40 infants with large VSD and PAB. Prior to surgery all had congestive heart failure, cardiomegaly, pulmonary plethora, and biventricular or right ventricular hypertrophy on electrocardiogram. At cardiac catheterization all had large VSD with pulmonary artery hypertension. No gradient between left ventricle and systemic artery was demonstrated. PAB was followed by improvement in all four children. Repeat catheterization at 4 to 11 years of age revealed that they had developed a significant (30 to 100 mm Hg) gradient across the left ventricular outflow tract. Although the etiology of the subaortic stenosis is not known, it is felt that the hypertrophied and possibly leftward deviated conal septum was impinging on the left ventricular outflow tract in three of the four. Since the subaortic stenosis was not suspected prior to the second catheterization, we feel that preoperative evaluation of children with VSD and PAB should include evaluation of the left ventricular outflow tract to be certain that no obstruction is present.