Adult T-cell leukemia lymphoma is extremely rare. We report a case of adult T-cell leukemia lymphoma involving lymph nodes and the liver. F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) imaging is a useful modality in detecting various tumors, including malignant lymphoma. We evaluated a patient with adult T-cell leukemia lymphoma using F-18 FDG PET imaging, which detected abnormal increased uptake in the left submandibular area, neck, clavicular area, axilla, mediastinum, liver, abdomen, and groin. The standardized uptake value of the highest FDG uptake was 20.5.