Intrinsic intrathoracic malformations are a rare group of congenital anomalies associated with high fetal and neonatal mortality rates. The antenatal sonographic appearance and the adequacy of diagnosis in 15 affected fetuses were evaluated. An accurate prenatal diagnosis was made in 12 cases; the precise nature of the intrathoracic defect was incorrectly categorized in two fetuses, and the defect was missed entirely in one affected fetus. Antenatal detection and characterization of intrinsic intrathoracic congenital malformations seems possible, but requires a high index of suspicion, familiarity with their sonographic appearances, and meticulous attention to detail.