Monoclonal gammopathy of undetermined significance (MGUS) is a highly prevalent condition with the possible risk of progression to multiple myeloma (MM) or a lymphoproliferative neoplasm in a small percentage of patients. Fluorine-18 fluorodeoxyglucose ( ¹⁸ F-FDG) positron emission tomography/computed tomography (PET/CT) or positron emission tomography/magnetic resonance imaging (PET/MRI) are imaging methods increasingly used in patients with MM. The aim of this communication is to underline that, taking into account current evidence-based data, compared to MM the role of ¹⁸ F-FDG PET/CT or PET/MRI in MGUS is still undetermined and more studies should be performed before suggesting ¹⁸ F-FDG PET/CT or PET/MRI for evaluation of MM progression in patients with MGUS.