Seventeen cases of different types of fetal thoracic and intrathoracic abnormalities were diagnosed prenatally by ultrasound: nonimmune hydrops (5 cases), diaphragmatic hernia (3), Potter's syndrome (3), chylothorax (1), exstrophy of the cloaca (1), the extreme form of prune-belly syndrome (2), cystic hygroma (1) and short rib polydactyly syndrome (Majevski type) (1 case). The ultrasonic features of nonimmune hydrops, diaphragmatic hernia, Potter's syndrome and cystic hygroma are well recognized by most experienced sonographers. The ultrasonic prenatal diagnosis of exstrophy of the cloaca, a very rare entity, has not been reported previously. The condition consists of a large infraumbilical anterior abdominal wall defect, lumbosacral myelomeningocele, and fetal ascites. The extreme form of prune-belly syndrome is associated with the absence of the abdominal wall musculature and marked dilatation of the urinary tract, presented ultrasonically as multiple large cysts occupying the distended fetal abdominal cavity. In exstrophy of the cloaca, prune-belly syndrome, Potter's syndrome and short rib polydactyly syndrome the chest abnormality is similar-extreme shortening of the thoracic cage, which has various causes. The differential diagnosis of all these entities and guidelines for their correct prenatal ultrasonic diagnosis are presented.