The pathway of abnormal embryonic development leading to congenital diaphragmatic hernia (CDH) is incompletely understood. Using a nitrofen-induced model of left CDH in rats, sequential stages of development were analyzed by scanning electron microscopy. Abnormal development patterns were observed in the cells comprising the posthepatic mesenchymal plate and the adjacent liver. The septum transversum did not appear to be involved. In this article, the authors theorize that a disturbed "balance of cell growth" is responsible for the creation of the diaphragmatic defect.