The role of FDG PET/CT in anal cancer is becoming increasingly important. At the time of initial staging, FDG PET/CT can detect the primary site of disease more frequently than CT, is sensitive for nodal and metastatic spread and alters staging in a significant number of patients. Indeed, the NCCN guidelines for anal cancer published in April 2012 recommend FDG PET/CT for therapy planning. Metabolic activity of primary anal cancer at presentation is a potential biomarker for predicting prognosis, treatment response and survival. More intensely FDG-avid primary malignancy is associated with a higher incidence of disease spread. Metabolic response following chemoradiotherapy is associated with improved survival. The aim of this paper is to provide an up-to-date pictorial review of FDG PET/CT in anal cancer at the time of staging and to illustrate its utility for determining response to therapy and detecting recurrent disease.