The original classification of neuroendocrine tumours proposed by Pearse was based on a common embryologic origin in the neuroectoderm. This is being replaced by other classifications based on results of modern techniques: secretory granules shown by electron microscopy, neuroendocrine tumour markers (NSE, chromogranin A, NPY ... ) shown by immunocytochemistry and blood measurements. Most endocrine tumours are single and sporadic, but in some patients they are multiple and/or occur as a familial disease such a multiple endocrine neoplasia or other disease, the transmission of which is autosomal dominant. This permits a more reliable classification of tumors, that can be used to determine their prognosis and response to therapy.