Positron emission tomography/computed tomography (PET/CT) represents a reliable promising tool in treatment response evaluation of new therapies beyond Imatinib in gastrointestinal stromal tumors (GIST). This narrative review aims to discuss the literature about the role of fluorine-18-fluorodeoxyglucose (18F-FDG) PET/CT in evaluating response in new tyrosine kinase inhibitors (TKI) and radiotherapy (RT) in GIST patients. A comprehensive literature search was performed to retrieve original studies published on PubMed, Scopus and Google Scholar databases. Eighteen studies including 382 patients with GIST were selected. Main findings of included studies are presented. Fluorine-18-FDG PET/CT may enhance performance in GIST management providing significant information in evaluation of treatment response and representing a strong predictor of clinical outcome.