Neurofibromatosis type 1 (NF1) is an autosomal dominant hereditary disorder. The pathogenesis of NF1 is suggested to be an alteration of the NF-1 gene, which normally functions as a tumor suppressor. A mutation of NF-1 causes the development of viable tumors in various sites. On the other hand, the synchronous manifestation of a gastrointestinal stromal tumor (GIST) and neuroendocrine tumor (NET) in the background of NF1 is extremely rare. This paper reports three cases treated with surgical intervention along with the long-term follow-up results. Three patients showed synchronous ampullary NET and GIST in association with NF1 supported by postoperative histopathologic analysis. Surgical treatments, such as pancreatoduodenectomy and local excision were applied. No recurrence occurred during the postoperative follow-up period of 10, 9, and 2.7 years. Synchronous GIST and NET in the background of NF1 is extremely rare, but the possible coexistence of other tumors in NF1 patients is relatively higher than that in the general population. Furthermore, both NETs and GISTs occurring in NF1 patients tend to be smaller in size compared to that in the general population. Therefore, when NF1 patients present with vague abdominal discomfort, close attention must be paid to identifying the coexistence of other neoplasms. (Korean J Gastroenterol 2019;74:227-231)