The ontogenesis of the endocrine pancreas has been a subject of controversy. The discussion essentially was about organogenesis and histogenesis of islets of Langerhans. Now, the endodermic origin seems well established by several experimental approaches. The variation of the aspects of the islets and of the number of endocrine cells are re-called as well as the functional activity during fetal life. Numerous neuropeptides have been found in endocrine pancreas, so the content of the different endocrine cell types is reviewed with respect to the classic hormones.