In lymphoma, FDG-PET is well established for staging and end-of-therapy response assessment. A promising more recent application is ‘early response assessment’, meaning that response to treatment is predicted using interim PET, i.e. PET during treatment. Timely assessment of forthcoming therapy failure in individual patients would have a profound impact on patient care by avoiding unnecessary toxicity and timely switching to potentially curative alternatives. Several observational studies have indicated that interim FDG-PET may be effective but inconsistencies prevail, especially in non-Hodgkin’s lymphoma (NHL). It is unclear to which extent these are due to differences in the timing of PET during therapy, different PET positivity criteria, different therapies and/or different subtypes of lymphoma. There is an urgent need to address these issues but this requires an integral approach using the results of various studies. Therefore, we propose to build a PETRA database for lymphomas.