Anal cancer is an uncommon tumor with an incidence of about one case per 100,000 in most countries. Its incidence seems to be increasing because of exposure to human immunodeficiency virus (HIV) and human papillomavirus (HPV). Traditional pretreatment evaluations include physical examination and CT imaging of the pelvis. Current treatment guidelines include fluorodeoxyglucose positron emission tomography integrated with computed tomography (FDG-PET/CT) as part of the standard pretreatment workup of patients diagnosed with anal cancer. At diagnosis, FDG-PET/CT is used to evaluate primary tumor size, lymph node status and to evaluate for distant metastases. FDG-PET/CT can also be used for radiation therapy treatment planning by clearly defining sites of metabolically active tumor. Posttherapy FDG-PET/CT to determine response to therapy is highly predictive of long-term clinical outcomes. This imaging modality can also be used to evaluate sites of recurrent disease. FDG-PET/CT is an imaging modality which greatly affects the management of patients with anal cancer.