- Based on the current medical literature, the worldwide incidence of neuroendocrine tumours (NETs) has seemed to increase; however, a systematic literature overview is lacking. This review aimed to collect all available data on the incidence of gastroenteropancreatic (GEP) NETs and population characteristics in order to establish their epidemiology. A sensitive MEDLINE search was performed. The papers were selected via a cascade process which restricted the initial pool of 7,991 articles to 31, using predefined inclusion and exclusion criteria. Original articles evaluating the incidence of sporadic GEP-NETs in regional, institutional and national registries were considered. The majority of data originates from the USA National Cancer Institute (NCI) Surveillance, Epidemiology, and End Results (SEER) database and from national cancer registries in Western Europe minimising selection bias. Age-adjusted incidence of GEP-NETs has steadily increased over the past four decades (1973-2007), increasing 3.65-fold in the USA and 3.8-4.8-fold in the UK. Incidence has changed variably from one anatomic site to another. The greatest increase in incidence occurred for stomach and rectum NETs, while the smallest increase was for NETs of the small intestine. There were gender and racial differences, which differed site by site and, in some cases, changed over time. Incidence rates of GEP-NETs have significantly increased in the last 40 years. Data are only available from North America, Western Europe and Japan. A site-by-site analysis revealed that for some NETs the incidence rate increased more than others.