Sotos syndrome is an autosomal dominant condition characterized by pre- and postnatal overgrowth (tall stature and macrocephaly), a typical facial appearance, advanced bone age, and developmental delay. The syndrome is caused by mutations or deletions of the nuclear receptor binding SET domain protein 1 (NSD1) gene, which encodes a histone methyltransferase implicated in the regulation of chromatin. Left ventricular noncompaction (LVNC), also called left ventricular (LV) hypertrabeculation, is a rare disorder classified as a primary genetic cardiomyopathy by the American Heart Association. This condition is characterized by an altered myocardial wall due to arrest of embryonic compaction of the loose interwoven meshwork that makes up the fetal myocardial primordium. The cardiac manifestations of this cardiomyopathy are variable, ranging from an absence of symptoms to a progressive deterioration in cardiac function, with heart failure, arrhythmias, and systemic thromboemboli. We describe two unrelated patients who had LVNC, as based on echocardiographic findings, and Sotos syndrome, as based on physical features and molecular analysis. To our knowledge, the literature contains no previous reports of concomitant LVNC and Sotos syndrome. In the light of these two cases, we suggest that patients with Sotos syndrome be evaluated for LVNC cardiomyopathy when being screened for heart defects. © 2011 Wiley-Liss, Inc.