Background: Most gastrointestinal stromal tumors (GIST) have either KIT or PDGFRA mutations. Neurofibromatosis type 1 pts caused by mutations in the NF1 gene have increased risk of GIST development, which may have no mutation in both genes. In this study, we analyzed clinical and pathological features of NF-1 associated GISTs. Methods: Study 1: We have screened 95 adults NF1 pts (age 31-66, 35 male and 60 female) by enhanced MDCT between 2003 and 2012. Study 2: We collected 1,184 sporadic GISTs from community hospitals in Japan between 2001 and 2010 retrospectively, and found 24 primary NF1-GISTs (1.7% of sporadic) and 2 recurrent NF1-GISTs, of whom clinicopathological features were analyzed. Results: Study1: By MDCT screening, we have found histologically confirmed 6 GISTs (4 males and 2 female; 6/1,000 NF1-persons/year) in the small intestine. Median age of NF1-GIST was 45, and five pts had multiple tumors, ICC hyperplasia in the normal intestine and no mutation in the KIT and PDGFRA genes. Study 2: Median age of 26 NF1-GIST (12 male and 14 female) was 58. 25 GISTs were located in the small bowel and one in the stomach. 17 pts had multiple GISTs and 9 pts single lesion. Pathologically, KIT was positive for all NF1-GISTs. 24 pts had spindle cell tumors and 2 had mixed or epithelioid. No mutation was found in the KIT and PDGFRA genes of 11 pts examined. Median values of mitosis (0/50HPF) and Ki67 (0.5%) were lower than those of sporadic GIST (3/50HPF and 2.5%). With media follow-up of 3.6 years, 8 pts had recurrences and 4 pts died of the disease. By western blotting, KIT was faintly phosphorylated but its downstream kinases including MEK, p44/22, AKT, mTOR, p38 and STAT3, were activated. Six pts received imatinib and had no response and, subsequently, 5 pts received sunitinib with 4 PD and 1 short-term SD. Conclusions: NF1-associated GIST is a rare entity of GIST and has distinctive features from conventional sporadic GISTs. KIT-targeted TKI appeared to be ineffective to recurrent and advanced NF1-GISTs.