Positron emission tomography (PET) imaging has become a very useful technique for staging and monitoring therapy response in lymphoma, providing unique information about the biological behavior of disease. Increased fluorine-18 fluorodeoxyglucose (FDG) uptake in lymphoma is based on elevated glycolysis and longer residence time of FDG in malignant cells compared with most normal tissues. The metabolic information provided by this technique suggests that FDG-PET may be more sensitive than the anatomical imaging modalities. Computed tomography (CT) is the principal imaging modality for the staging and restaging of lymphoma. Nonetheless, this technique has significant shortcomings, particularly in the post-therapy setting. Gallium-67 scintigraphy has played an important role in monitoring response to therapy and follow-up of patients; however, the sensitivity of 67Ga depends on the subtype of lymphoma and the size and location of disease. Published results strongly indicate that FDG-PET is superior to 67Ga imaging and may be equal or superior to CT for the detection of nodal as well as extranodal involvement in lymphoma.