Congenital diaphragmatic eventration is an abnormal elevation of the diaphragm resulting from failure of muscle fibers to develop during gestation. A mediastinal shift to the contralateral side may cause significant compression of the affected chest contents, resulting in compromised pulmonary function, especially when both sides are involved. Differentiating between congenital diaphragmatic eventration and congenital diaphragmatic hernia is very difficult but important because eventration has a better perinatal outcome than diaphragmatic hernia has. This report discusses a case of congenital diaphragmatic eventration that was initially diagnosed by prenatal sonography as a diaphragmatic hernia on the left side. In this case, the correct diagnosis was made at the time of surgery shortly after the infant's birth. The defect was repaired by plication, and the infant's outcome was favorable. Although the initial diagnosis was incorrect in this case, the use of sonography can aid in the prenatal detection and diagnosis of congenital diaphragmatic anomalies.