Adult T-cell leukemia/lymphoma (ATLL) is a rare and, often, aggressive lymphoma that is causally linked to chronic infection with human T -cell lymphotropic virus type 1. Four subtypes have been described: acute, lymphomatous, chronic, and smoldering. The acute and lymphomatous subtypes comprise the aggressive variants. Patients often require extensive supportive care designed to manage hypercalcemia, tumor lysis syndrome, and infectious complications. Prognosis is poor for the aggressive subtypes, and treatment strategies have traditionally focused on antiviral therapy with zidovudine and interferon-alfa, as well as combination chemotherapy. Novel therapeutic approaches include monoclonal antibody therapy with brentuximab vedotin, anti-CC chemokine receptor 4 therapy with mogamulizumab, and immunomodulatory therapy with lenalidomide.