The autosomal dominant association of upper extremity skeletal defects with congenital heart disease is known as the Holt-Oram syndrome. We reviewed our experience with 39 affected patients of whom 15 were considered new mutations. Wide varieties of skeletal defects and congenital heart disease were observed, and the severity of skeletal involvement did not parallel that of cardiac disease. These patients demonstrate four previously unemphasized points: (1) There is a striking asymmetry of skeletal involvement, with the left side more severely affected. (2) Patients with skeletal defects alone can transmit both skeletal and cardiac defects to their children. (3) Hypoplastic peripheral vessels may be an associated abnormality and can result in difficulty with cardiac catheterization. (4) Electrocardiographic changes of terminal conduction delay in the right anterior chest leads were nor uniformly present in patients with otherwise typical secundum atrial septal defects.