Abstract
Radiological analysis of the limb deformities of thalidomide children reveals evidence of a sensory neuropathic process. Based on this, a hypothesis of neural crest injury is suggested as the underlying pathogenetic mechanism of many congenital malformations. Using a simple concept of four different modes of growth in the embryo, the hypothesis appears to explain both skeletal and visceral deformities. Experimental and pathological evidence is presented in its support, and a rational approach to congenital defect syndromes is suggested.