Background and Aim. Fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) is well recognized as a powerful diagnostic tool in the initial staging of patients with multiple myeloma (MM). The aim of this paper is to perform a systematic review about the usefulness of FDG-PET or PET/CT in evaluating the response to treatment in patients with MM. Methods. The scientific literature about the role of FDG-PET or PET/CT in evaluating the response to treatment in patients affected by MM was systematically reviewed. Results. Ten studies about the role of FDG-PET or PET/CT in evaluating treatment response in MM were retrieved and discussed. Conclusions. FDG-PET or PET/CT seems to be helpful in assessing the response to treatment in patients with MM and in the evaluation of possible sites of recurrent or progressive disease.