To evaluate the sensitivity of two-dimensional sector scan (2DSS) for detecting ventricular septal aneurysms (VSA) associated with ventricular septal defects, we studied thirteen patients, one week to thirteen years of age, with positive M-mode findings of VSA. The criteria for M-mode diagnosis of VSA were multiple echoes within the right ventricle resembling systolic anterior motion of the tricuspid valve (TV). On 2DSS the aneurysm could be seen in several tomographic planes, but most regularly in long axis and apical views; in systole, the aneurysm prolapsed into the right ventricle below the septal leaflet of the TV. We compared these noninvasive techniques to the cineangiographic findings in all thirteen patients. When compared to cineangiograms, 2DSS were in agreement in all cases; there were four false positive M-mode studies. M-mode is thus useful as a screening test (no false negatives), but needs confirmation from 2DSS which appears as specific as cineangiography in detecting VSA. The 2DSS should be a valuable method for diagnosing and following the course of VSA associated with VSD, without the need for cardiac catheterization.