Positron emission tomography is a functional imaging modality that capitalizes on biochemical changes within tumour cells to localize these changes within the body. As a functional imaging tool, unlike an anatomical imaging tool such as CT, it does not require enlargement of lymph nodes affected by disease but does require sufficient numbers of tumour cells to be present with altered biochemical function to visualize these disease sites. These changes are most commonly monitored using a glucose mimic fluorodeoxyglucose which is not only taken up into tumour cells but is trapped within these cells owing to alterations of the hexokinase and dephosphorylase enzymes. This review examines the current role of FDG PET imaging in patients with Hodgkins and Non-Hodgkins lymphoma and also speculates on future roles for this imaging modality.