Adult T-cell lymphoma/leukemia (ATL) is a rare and aggressive peripheral variant, specific to T-cell non-Hodgkin's lymphoma. One of the criteria for the diagnosis of ATL is positive serology for human type 1 lymphotropic virus (HTLV). This study reports a rare presentation of ATL in a 36-year-old female patient. The diagnosis was obtained by means of histopathologic and immunohistochemical aspects (positivity for CD3 and negativity for ALK and EMA, with Ki-67 of 80%) and positivity in the anti-HTLV exam. The patient underwent 3 chemotherapy sessions. After an emergency hospitalization, the patient died. In view of its aggressiveness and its potentially fatal behavior, it is important to know the signs and symptoms of lymphoma so the diagnosis can be made early.