Positron emission tomography (PET) is widely used in the diagnosis and response assessment after first-line treatment of Hodgkin’s lymphoma (HL). For the approximately 30 % of patients who relapse or have refractory disease, PET can provide valuable prognostic information during second-line therapy, at the time of autologous stem cell transplant (ASCT). Retrospective studies performed over the past decade have consistently found a significant association between a positive PET scan after salvage chemotherapy for HL and progression-free and overall survival after ASCT. In fact, the predictive value of pre-transplant PET appears higher than that of more traditional clinical risk factors. Unfortunately, there is little data to recommend the best treatment course for patients who have a positive pre-ASCT PET, and few studies have addressed the role of PET in other relapsed/refractory HL settings.