Malignant lymphomas are lymphoproliferative disorders arising in both lymphoid tissue and non-lymphoid organ systems. Treatment rarely is surgical, and currently relies on a combination of chemotherapy and radiation therapy. The role of imaging is to determine the spread of the disease, to identify targets and to assess therapeutic response. Imaging techniques mainly use morphological criteria, and may underestimate infiltrative disease, as observed in bones. The frequent presence of residual masses after treatment usually prevents classification of patients as complete response. Over time, positron emission tomography (PET) with F18-fluorodeoxyglucose (FDG) has become a prominent part of the workup at diagnosis and during follow-up. Recently, PET has been integrated in the revised response criteria for malignant lymphoma.