Adult T-cell leukemia/lymphoma (ATLL) is a rare T-cell lymphoproliferative disease associated with human T-cell leukemia virus type 1. There are four subtypes of ATLL: smoldering, chronic, lymphoma and acute. All subtypes can exhibit extranodal involvement. Hepatic infiltration occurs in the chronic, lymphoma and acute types of ATLL, but symptoms are rare. We report the case of a 32-year-old patient with acute-type ATLL and atypical severe hepatic dysfunction at diagnosis. At first, the patient presented with non-specific signs and symptoms, including severe abdominal pain, jaundice, hepatosplenomegaly, ascites and small lymphadenopathies, as well as leukocytosis, which was initially considered reactive. After excluding acute abdomen, the patient was referred to the hematologist. The diagnosis of acute-type ATLL was unexpectedly suggested by peripheral blood smear and confirmed by immunophenotyping by flow cytometry. Multiple causes of liver dysfunction, including hepatic infiltration, paraneoplastic syndrome, infectious diseases, extrahepatic compression, hemophagocytic syndrome, alcoholic liver disease and drug- induced hepatotoxicity, were taken into account. Considering the concurrence of ATLL diagnosis with liver dysfunction, the favorable clinical and biological evolution after specific hematological treatment, and the absence of imaging supporting other possibilities, we concluded that diffuse hepatic infiltration was the most probable cause. When evaluating hepatic dysfunction, considering a broad differential diagnosis is crucial. While it is uncommon, lymphoma should be included in the list of potential causes.