Simple SummaryNeuroendocrine tumours in the small intestine (SI-NETs) may be cured with surgery, and oncological treatment may prolong survival. The trend in survival may improve over time due to advances in surgical or oncological treatment or if the disease is diagnosed at an earlier stage. We examined 242 patients with SI-NETs diagnosed from 2005 to 2021 and compared the first (2005 to 2012) and second (2012 to 2021) halves of the cohort concerning disease severity, surgical and oncologic treatment, and long-term survival. Overall survival was longer in the second period, particularly in the first year after diagnosis. This could not be explained by SI-NETs being diagnosed at an earlier stage or major differences in oncological treatment. Several observations suggested that the surgical quality could be better in the second period, as the number of lymph nodes and primary tumours retrieved during surgery was higher.AbstractImproved surgical resection and oncological treatment, or an earlier diagnosis may increase survival in small intestinal neuroendocrine tumours (SI-NETs), but only few studies have examined survival trends. We aimed to examine the trend in overall survival and associated factors in SI-NET patients. All patients with SI-NETs at a regional hospital from June 2005 to December 2021 (n= 242) were identified, and the cohort was divided in half, constituting a first period (until November 2012) and a second period (from November 2012). Disease and treatment characteristics, including European Neuroendocrine Tumour Society (ENETS) stage, surgery, oncological treatment and survival, were recorded. The majority (n= 205 (84.7%)) were treated surgically and surgery was considered curative in 137 (66.8%) patients. Median survival was longer in the second period (9.0 years 95% CI 6.4–11.7 in the first period vs. median not reached in the second period,p= 0.014), with 5-year survival rates of 63.5% and 83.5%, respectively. ENETS stage and oncological treatment did not differ between the periods, but factors associated with surgical quality, such as lymph node harvest and resection of multiple SI-NETs, were significantly higher in the second period. Age, ENETS stage, time period and tumour resection were independently associated with survival in a multivariate analysis.