Hodgkin lymphoma, even in advanced-stage, is a highly curable malignancy, but treatment is associated with short-term toxicity and long-term side effects. Early predictive markers are required to identify those patients who do not require the full-length standard therapy (and thus qualify for therapy de-escalation) and those patients who will not be cured by standard therapy (and thus qualify for therapy escalation). Multiple trials have assessed the value of 18 F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) after a few cycles of chemotherapy (also known as 'interim FDG-PET') in predicting outcome in advancedstage Hodgkin lymphoma. Furthermore, multiple interim FDG-PET-adapted trials, in which patients with positive interim FDG-PET scans are assigned to escalated therapies, and patients with negative interim FDG-PET scans are assigned to de-escalated therapies, have recently been published or are currently ongoing, with generally heterogeneous results. The present article reports the currently available evidence (and controversies) on the prognostic value of interim FDG-PET in advanced-stage Hodgkin lymphoma in patients with positive and negative interim FDG-PET findings following continuation of standard chemotherapy or escalated/de-escalated therapy. Hodgkin lymphoma is one of the most frequently occurring malignancies in young adults aged 20-40 yr, whereas a second incidence peak is observed in people aged >55 yr (1). Early-stage Hodgkin lymphoma is usually treated with two to three cycles of adriamycin, bleomycin, vinblastine and dacarbazine (ABVD) followed by radiation therapy (RT), whereas there is less consensus on the optimal treatment of advanced-stage Hodgkin lymphoma, in which six to eight cycles of ABVD or six to eight cycles of a more intense regimen of bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine and prednisone (BEACOPP) are proposed (2). An important question in treating Hodgkin lymphoma is whether intensified chemotherapy should be applied upfront or reserved for patients with resistance to first-line therapy. In advancedstage Hodgkin lymphoma, the administration of six to eight cycles of ABVD has been reported to result in a long-term progression-free survival (PFS) of approximately 75% (3-6), whereas with upfront BEACOPP chemotherapy, the long-term PFS is approximately 85% (7-10). However, upfront BEACOPP chemotherapy is associated with an increased toxicity profile compared to ABVD therapy (7, 10). Furthermore, whether upfront BEACOPP will result in an improved overall survival (OS) compared to ABVD chemotherapy has not been consistently proven, with heterogeneous results among studies (7,8,(10)(11)(12). Therefore, there are strong arguments to reserve intensified treatments as second-line therapy for patients in whom standard firstline ABVD treatment fails, rather than exposing the entire population to an intensified treatment as would happen in case of upfront BEACOPP chemotherapy.To reduce toxicity and maximise patient outcome, id...