Human T-lymphotropic virus-1 (HTLV-1) can cause adult T-cell leukemia/ lymphoma (ATL/L), which is a rare and aggressive type of blood cancer.Herein, we report a case of ATL/L in a middle-aged man with unusual jaw presentations. The patient presented with mandibular, maxillary and palatal bony hard expansion, accompanied by generalized tooth mobility six months prior to admission to the Department of Oral Medicine. The panoramic radiograph showed generalized rarefaction of jaw bones. After laboratory examinations and bone marrow aspiration, ATL/L was diagnosed in association with HTLV-1. The patient underwent chemotherapy.Although the majority of infections associated with HTLV-1 are asymptomatic, some patients may develop blood diseases such as ATL/L and neurological disorders, mainly HTLV-1 associated myelopathy and tropical spastic paraparesis. ATL/L is a rare hematological malignancy in oral cavity that should be included in the differential diagnosis of cases with jaw swelling or generalized demineralization. Serum levels of anti-HTLV-1 antibodies should be examined in suspicious patients, particularly in endemic regions.