Background: We conducted a population-based study to establish the incidence, treatment and overall survival over time of patients with small bowel adenocarcinoma.Material and methods: All patients diagnosed with small bowel adenocarcinoma in the Netherlands between 1999 and 2013 were included (n=1775). Age-standardized incidence rates were calculated per 100 000 person-years using the European standardized population rate. The influence of patient and tumor characteristics on the administration of chemotherapy was analyzed by means of a multivariable logistic regression analysis. The Cochran-Armitage trend test was conducted to evaluate trends in treatment and survival and the Cox proportional hazards model was used to identify prognostic factors of overall survival.Results: The incidence of small bowel adenocarcinomas increased, mainly due to an almost twofold increase of duodenal adenocarcinomas. Patients with locoregional duodenal tumors were less likely to undergo surgery (58%), towards 95% of the locoregional jejunal and ileal tumors (p<0.0001). The use of chemotherapy doubled for adjuvant (7-15%) and palliative chemotherapy (19-37%). Median overall survival of patients with locoregional disease increased from 19 to 34 months (p=0.0006), whereas median overall survival of patients with metastatic disease remained 4-5 months. Favorable prognostic factors for prolonged survival in locoregional disease, identified by multivariable survival analysis, included age<60 years, tumor stage I or II, diagnosis in 2009-2013, surgical treatment and chemotherapy. Favorable prognostic factors for prolonged survival in metastatic disease were age<50 years, jejunal tumors, surgical treatment and chemotherapy.Conclusion: Small bowel adenocarcinomas are rare tumors with an increasing incidence. The administration of adjuvant and palliative chemotherapy doubled, but median overall survival only increased for patients with locoregional disease. Given the rarity and dismal prognosis, it is important to develop international studies to determine the optimal treatment for these patients.