Adult T cell lymphocyte leukemia/lymphoma (ATLL) is a subtype of T-cell lymphoma caused by infection of the human T-cell lymphotropic virus type 1 (HTLV-1); which generates a pro-viral integration into the host DNA, resulting in a clonal expansion of T lymphocytes. We present the case of a 20-year-old woman who developed multiple lymphadenopathies, hepatosplenomegaly and fever, serum positivity for HTLV-1 and proviral integration in the host DNA, demonstrated by polymerase chain reaction (PCR). Immunohistochemistry of lymphoid node was positive to CD4+ and CD8+ T cells. ATLL has been described in all HTLV-1 endemic areas, however, there are differences in the mean age of its presentation in such areas: 40 to 50 years in South America, 60 years in Japan. We showed one of few reported cases of the lymphoma type of ATLL in young adults.