BACKGROUND AND OBJECTIVES: In order to receive the most appropriate therapy, patients with Hodgkin's lymphoma (HL) must be accurately stratified into different prognostic staging groups. Computed tomography (CT) plays a pivotal role in the conventional staging. The aim of the present study was to investigate the value of positron emission tomography using 2-[18F]fluoro-2-deoxy-D-glucose (FDG-PET) and combined FDG-PET/CT for the staging of HL patients, and the impact on the choice of treatment. DESIGN AND METHODS: Ninety-nine consecutive, prospectively included patients had FDG-PET and CT in their staging work-up. Sixty-one of the 99 patients had combined FDG-PET/CT. A standard of reference for each nodal region and organ was determined using all available information including scan results, histology and a minimum of one year's clinical follow-up data. The lack of a satisfactory diagnostic gold standard limits the reliability of accuracy calculations. RESULTS: FDG-PET would have upstaged 19% of patients and downstaged 5% of patients, leading to a different treatment in 9% of patients. For FDG-PET/CT, the corresponding figures are 17%, 5%, and 7%. In nodal regions, the sensitivity of FDG-PET and FDG-PET/CT seemed higher than that of CT (92% and 92% vs. 83%). FDG-PET identified more false positive nodal sites than did CT and FDG-PET/CT (1.6% vs 0.7% and 0.5%). FDG-PET and FDG-PET/CT were highly sensitive for evaluating organs (86% and 73%) while CT detected 37% of involved organs. INTERPRETATION AND CONCLUSIONS: FDG-PET and FDG-PET/CT have a substantial potential impact on staging and choice of treatment and the methods tend to upstage rather than downstage patients. FDG-PET and FDG-PET/CT seem to have a higher diagnostic accuracy than CT in the staging of HL. However, care should be taken so patients with an excellent prognosis and at risk of over-treatment do not receive more intensive treatment because of these staging methods.