The role of F-18-fluorodeoxyglucose positron emission tomography (FDG-PET) in the assessment of lymphoma patients is well established, and PET is routinely used for initial staging, early evaluation of treatment response, and identification of disease relapse. The early evaluation of response to therapy (interim PET) has been reported to be an accurate predictor of progression-free survival, and end-treatment PET has been suggested to be unnecessary if interim PET results are negative. We report on a patient with Hodgkin's disease with a positive PET scan at presentation and a negative interim PET (carried out after three cycles of adriamycin, bleomycin, vinblastine, and dacarbazine; ABVD). Despite uncomplicated clinical course, end-treatment PET (following six cycles) was positive, showing a very early relapse. For this reason, patient underwent further treatment; however, a complete remission was not obtained, and a poor prognosis is expected. This case testifies the possibility of early relapse of lymphoma even in the case of negative interim PET; it also supports the usefulness of end-treatment PET scan in lymphoma patients.