Subaortic stenosis is rarely mentioned as a lesion that may be associated with a ventricular septal defect. We have encountered 4 patients with discrete subaortic stenosis adjacent to a ventricular septal defect, all of whom posed significant problems in diagnosis. In all 4 patients the subaortic stenosis was silent clinically and in 3 cases the obstruction was also not detected at the initial cardiac catheterization and angiocardiography. In the latter 3 cases, after surgical closure of the ventricular septal defect, there was a loud systolic murmur initially thought to be due to a small residual ventricular septal defect. In time, the clinical findings became more typical of isolated subaortic stenosis. In each of these cases the obstruction was verified at cardiac catheterization with peak systolic pressure gradients of 145, 45, and 70 mmHg. During reoperation, a discrete subaortic shelf was found opposite the patch used to close the ventricular septal defect. In the 4th case, the subaortic stenosis was unsuspected by clinical evaluation but was diagnosed by echocardiography as well as at cardiac catheterization, and both the ventricular septal defect and subaortic stenosis were corrected at the initial operation. A discrete subaortic shelf situated adjacent to a ventricular septal defect may be "silent," producing minimal, if any, pressure gradient and may pose diagnostic difficulties. Failure to recognize such a shelf and to remove it at the time of surgical closure of the ventricular septal defect, may result in the creation of a severe subaortic obstruction.