Purpose: The aim of this systematic review and meta-analysis was to compare the role of FDG-positron emission tomography (PET) or PET/computed tomography (CT) with conventional imaging in the detection of primary and nodal disease in anal cancer, and to assess the impact of PET or PET/CT on the management of anal cancer. Methods: A systematic review of the literature was performed. Eligible studies included those comparing PET or PET/CT with conventional imaging in the staging of histologically confirmed anal squamous cell carcinoma (SCC), or studies that performed PET or PET/CT imaging to assess response following treatment. Results: Twelve studies met the inclusion criteria. For the detection of primary disease, CT and PET had a sensitivity of 60 % (95 % confidence interval [CI] 45.5–75.2) and 99 % (95 % CI 96–100), respectively. Compared with conventional imaging, PET upstaged 15 % (95 % CI 10–21) and downstaged 15 % (95 % CI 10–20) of nodal disease. This led to a change in nodal staging in 28 % of patients (95 % CI 18–38). When only studies performing contemporary PET/CT were considered, the rate of nodal upstaging was 21 % (95 % CI 13–30) and the TNM stage was altered in 41 % of patients. Following chemoradiotherapy, 78 % (95 % CI 65–88) of patients had a complete response on PET. Conclusion: Compared with conventional imaging, PET or PET/CT alters the nodal status in a sufficient number of cases to justify its routine use in the staging of patients with anal SCC. Although uncommon, the incidence of anal squamous cell carcinoma (SCC) is increasing.1–3 This is largely due to the greater prevalence of known risk factors—human papillomavirus (HPV) and human immunodeficiency virus (HIV). FDG-positron emission tomography (PET) with or without computed tomography (CT) is an integral part of the management of a number of malignancies. These include mucosal SCC of the head and neck as well as the cervix, two tumors with similarities to anal canal SCC both commonly caused by HPV and managed with definitive chemoradiotherapy (CRT).4,5 Although utilization of PET in anal cancer is increasing, evidence for its influence on the management of this malignancy is limited. The current National Comprehensive Cancer Network (NCCN) guidelines recommend PET/CT be considered in the staging of patients with node-positive disease or T3–4 primary tumors, noting that routine use of PET/CT for staging has not been validated.6 The panel did not recommend PET/CT for assessing treatment response due to concerns it may prompt abdominoperineal resection (APR) in patients with slowly responding disease. Instead, regular digital rectal examination (DRE) should be performed and, for patients with stage III–IV disease, annual CT of the chest/abdomen/pelvis. The recently updated European Society for Medical Oncology (ESMO) clinical practice guidelines for anal cancer7 include PET as an “optional but often recommended” modality in the work-up of patients. They note that “several studies have shown that FDG-PET/CT can alter staging in approximately 20 % of cases”. Following definitive CRT, the guidelines make no recommendation regarding the use of PET due to a paucity of data. We collated the existing data on the use of PET in anal SCC in order to better define its use in the management of this disease. Our review will focus on the comparative staging of PET or PET/CT with conventional imaging, as well as the value of PET or PET/CT following treatment.