Human T-lymphotropic virus type I (HTLV-I) is endemic in the Caribbean region, south-western Japan and Africa, and is associated with tropical spastic paraparesis and adult T-cell leukaemia/lymphoma (ATLL). Cutaneous forms of ATLL are sometimes indistinguishable from other cutaneous T-cell lymphomas (CTCL). We report a woman living in a non-endemic area for HTLV-I, with no risk factors for viral infection, who developed mycosis fungoides-like ATLL. The findings underline the usefulness of molecular biological techniques in distinguishing between mycosis fungoides and ATLL. We emphasize the need to establish the HTLV-I status of patients with CTCL, even in HTLV-I non-endemic areas, not only to establish a preventive policy in these countries, but also to further our knowledge of the lymphoproliferation spectrum associated with human retroviruses.