Indolent T-lymphoblastic proliferation has been rarely reported in the upper aerodigestive tract. The lymphoid cells associated with this condition have the morphological and phenotypical features of immature thymocytes. However, their pathogenesis and biology are unknown. We present an unusual type of tumor infiltrating lymphocytes in a case with hepatocellular carcinoma, presumed to be a T-lymphoblastic proliferation. A 58-yr-old female patient presented with indigestion and a palpable epigastric mass. The abdominal computed tomography revealed a mass in the S6 region of the liver. A hepatic segmentectomy was performed. Microscopic examination showed dense isolated nests of monomorphic lymphoid cells within the tumor. Immunohistochemically, the lymphoid cells were positive for CD3, terminal deoxymucleotide transferase (TdT) and CD1a. In addition, they showed dual expression of CD4 and CD8. The polymerase chain reaction used to examine the T-cell antigen receptor gamma gene rearrangement showed polyclonal T-cell proliferation. This is the second case of hepatocellular carcinoma combined with indolent T-lymphoblastic proliferation identified by an unusual tumor infiltrating lymphocytes.