Extranodal lesions in Hodgkin disease may develop and spread to virtually any organ system, simulating other neoplastic or infectious diseases. It is important to determine whether extranodal involvement represents a primary manifestation or dissemination of systemic disease, which has a poorer prognosis. Computed tomography (CT) is the preferred modality, although ultrasonography and magnetic resonance (MR) imaging may also be helpful. CT is superior to conventional radiography in assessing chest disease, although MR imaging is more sensitive than CT in detecting chest wall involvement. CT is preferred for evaluating hepatic lymphoma and has proved particularly valuable in diagnosing gastric lymphoma and detecting renal or perirenal masses. CT and MR imaging are equally effective in detecting brain Hodgkin disease; however, the latter is superior in the detection of extracerebral tumor deposits in the subdural or epidural space. MR imaging is also preferred for evaluating meningeal and spinal cord involvement. Both MR imaging and CT allow excellent assessment of bone texture and accurate analysis of tumoral bone invasion, but MR imaging is superior in demonstrating bone marrow infiltration, and CT is superior in delineating the extent of cortical bone destruction. In the future, metabolic positron emission tomography may provide more information about extranodal lymphoma than do the current imaging modalities.