BACKGROUND Type 1 neurofibromatosis (NF1) is known to be associated with not only neurogenic tumors but also gastrointestinal (GI) neoplasms. However, there are few reports on vascular lesions and the incidence is unknown. CASE REPORT We report here the case of a 45-year-old woman with a history of NF1 referred to our hospital for the purpose of detailed examination for positive fecal occult blood test. On the basis of the investigation reports, she was diagnosed with a neuroendocrine tumor (NET)-G1. We planned a subtotal stomach-preserving pancreaticoduodenectomy. The abdominal structures, including the vascular system, were abnormally fragile, and it was very difficult to achieve satisfactory hemostasis. The total amount of intraoperative blood loss was 7580 mL. Fulminant intra-abdominal bleeding occurred on postoperative day (POD) 3. Urgent angiography showed a rupture of the gastroduodenal artery. Transarterial embolization was performed, but the patient died of multiorgan failure on POD5. On histological examination, neurofibroma cells proliferating into the surrounding blood vessels were seen; moreover, immunohistochemistry staining with S-100 antibody showed positive neurofibroma cells surrounding the vascular wall. The pathological diagnosis was duodenal NET-G1 with multinodal involvement. CONCLUSIONS This case is a rare presentation of a NET with multiple gastrointestinal stromal tumors associated with NF1, which led to a fatal outcome due to the extreme fragility of the vessel walls. Since patients with NF1 might have vulnerable vessel walls, adequate surgical preparation for major surgical treatment is necessary.