Early identification of refractory lymphoma patients provides a basis for stratification between responders to standard approaches and non-responders who may benefit from an early change to an alternative treatment strategy.Metabolic or molecular imaging with fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG-PET) has emerged as a powerful imaging modality for diagnosis, staging, and therapy monitoring of a variety of cancers. The primary hypothesis of the present study is that early response can be pinpointed by PET reflecting both tumor burden and activity, as a surrogate for final outcome. An increasing number of studies have suggested the potential role of 18F-FDG PET in the staging and monitoring of lymphomas. The optimal timing of PET scans and the potential role of quantitative PET using SUV to assess response to chemotherapy remain to be defined. Confirmation of very early 18F-FDG-PET as a significant predictor of treatment response in a homogenous group of aggressive lymphoma patients would potentially change the prognosis of the patient by allowing earlier use of alternative therapies and discontinuation of therapy that will not lead to a significant tumour response.