The aim of this systematic review was to examine published data about the potential role of Fluorine-18-fluorodeoxyglucose positron emission tomography or positron emission tomography/computed tomography ( ¹⁸ F-FDG PET or PET/CT) in patients affected by mantle cell lymphoma (MCL). A comprehensive computer literature search of Scopus, PubMed/MEDLINE, and Embase databases was conducted, including articles indexed up to November, 2019; 25 studies or subsets in studies analyzing the value of ¹⁸ F-FDG PET or PET/CT in patients with MCL were eligible for inclusion. From the analyses of the selected studies, the following main findings are described: (1) MCL are ¹⁸ F-FDG-avid in most of cases, especially nodal lesions, but bone marrow and gastrointestinal disease localizations have low ¹⁸ F-FDG avidity; (2) ¹⁸ F-FDG PET/CT seems to be helpful in staging setting, showing a better diagnostic performance than conventional imaging and a positive impact on clinical stage; (3) ¹⁸ F-FDG PET/CT is useful in evaluating treatment response, especially after chemotherapy and transplantation; and (4) metabolic response after therapy seems to have a prognostic role. Despite several limitations affecting this analysis, especially related to the heterogeneity of the studies included, MCL is an ¹⁸ F-FDG-avid lymphoma in most of the cases, with the exception of bone marrow and gastrointestinal disease. Moreover, ¹⁸ F-FDG PET/CT seems to be useful in evaluating treatment response and prognosis.