Acquired maxillo-facial deformities and in particular those related to problems of facial expression are nevertheless influenced by certain hereditary factors, amongst which the constitutional type or the temperament of the individual play a major role. Morpho-psychology (L. Corman), or the art of relating physical details (especially the shape and characteristics of the face) with psychological state demonstrates correlations between the type of deformity and that of the temperament and explains them. After a brief review of the essential principles of morpho-psychology, the authors study a number of special morpho-psychological types presenting with a significant frequency maxillo-facial deformities, themselves special, and which for this reason they call "morpho-psychological types with a high orthodontic risk". They conclude that it would appear that insufficient importance is attributed at present to psychological factors in the aetiopathogenesis of dysmorphoses and feel that an overall approach to the deformed child is indispensable to progress in the specialty.