The angiodysplasias represent a "disease of the vasculo-connective tissue system", the cells of the primitive area vasculosa being simultaneously histoblastic and haemoblastic. This accounts for the many facets of the clinical picture and the nosology. The slightest deviation in ontogenetic organization involves one or more malformations which embryology unfolds in the course of the various stages of development, provided that the importance of vasculo-connective tissue correlations and hydraulic factors is never forgotten. The problem of nosological classification is very difficult ; many have attempted it, including the School of Nancy with Kissel and André, that of Milan with Puglionisi, that of Schobinger and Leu, that of J. Natali... it remains to classify the clinical picture presented in one or another list.