Positron emission tomography (PET) imaging using [F-18]fluorodeoxyglucose (FDG) has become a useful imaging modality in the staging and treatment evaluation algorithm for lymphoma, providing unique metabolic information. Increased FDG uptake in lymphoma tumor masses is a function of increased anaerobic metabolism and longer residence time of FDG in malignant cells relative to most normal tissues. The information provided by FDG-PET appears to result in greater sensitivity compared to anatomic imaging modalities, particularly computed tomography (CT). Over several decades CT has been the principal imaging modality for the staging and restaging of lymphoma, although it can have significant shortcomings stemming from its sized-based criteria, particularly in the post-therapy setting. Gallium-67 (Ga-67) scintigraphy has played an important role in monitoring response to therapy; however, the sensitivity of Ga-67 depends on histologic subtype of lymphoma, size, and location of disease. Published results suggest that FDG-PET is superior to Ga-67 imaging and equal or superior to CT for the detection of nodal and extranodal lymphoma at initial staging. Furthermore, persistent FDG uptake during and after chemotherapy has a high sensitivity and specificity for prediction of subsequent relapse. While in some cases FDG-PET imaging can yield findings that prompt a change in treatment strategy, prospective studies are necessary to better establish the ability of routine FDG-PET imaging to impact therapeutic outcomes for patients with lymphoma.