Neuroendocrine tumours of the gastrointestinal tract are rare, but challenging. In addition, they are models in tumour biology. The biochemistry used for diagnosis and control of the therapy has expanded considerably over the past decades. Today, the diagnosis comprises examination of genes in hereditary tumour syndromes as well as measurement of protein markers and specific peptide hormones in a biogenetic context. The infrequency and demand for analytical know-how make the case for centralization of diagnostic examinations.