Gastrointestinal stromal tumour (GIST) is a disease of older adults and is dominated by KIT/PDGFR mutations. In children, GIST is rare, predominantly occurs in girls, has a stomach location and generally lacks KIT/PDGFR mutations. For young adults (YA), aged 18 to 40 years, the typical phenotypic and genotypic patterns are unknown. We therefore aimed to describe the clinical, pathological and molecular characteristics of GIST in in YA. YA GIST patients registered in the Dutch GIST Registry (DGR) were included, and data were compared to those of older adults (OA). From 1010 patients in the DGR, 52 patients were YA (54% male). Main tumour locations were stomach (46%) and small intestine (46%). GIST genetic profiles were mutations in KIT (69%), PDGFRA (6%), SDH deficient (8%), NF1 associated (4%), ETV6-NTRK3 gene fusion (2%) or wildtype (10%). Statistically significant differences were found between the OA and YA patients (localisation, syndromic and mutational status). YA presented more often than OA in an emergency setting (18% vs. 9%). The overall five-year survival rate was 85%. In conclusion, YA GISTs are not similar to typical adult GISTs and also differ from paediatric GISTs, as described in the literature. In this series, we found a relatively high percentage of small intestine GIST, emergency presentation, 25% non-KIT/PDGFRA mutations and a relatively good survival.