Adult T-cell leukaemia-lymphoma (ATL) is a malignancy of peripheral T lymphocytes caused by human T-lymphotropic virus type I (HTLV-1), and its prognosis is poor. There are an estimated 5 million to 20 million HTLV-1 infected individuals worldwide; their lifetime risk of developing ATL is 3–5%, and high HTLV-1 proviral loads have been shown to be an independent risk factor. Recent advances in the treatment of ATL are the introduction of treatment targeted against CC chemokine receptor 4 (CCR4), which is abundantly expressed on most ATL cells, and allogeneic haemopoietic stem-cell transplantation for aggressive ATL. Promising outcomes are also reported with early intervention for indolent ATL with interferon α and zidovudine. Clinical trials should incorporate a validated prognostic index to assess the results, because of the difficulties associated with undertaking large-scale trials and significant diversity of clinical features with ATL, even in the same clinical subtypes (acute, lymphoma, chronic, and smoldering).