Intravascular malignant lymphomatosis (IML) is an unusual condition characterized by proliferation of lymphoma cells exclusively within the blood vessels. Most of the cases reported are of B-cell origin. We report a rare case of T-cell IML probably associated with human T-lymphotropic virus (HTLV-1) infection. The present case suggests that T-cell lymphoma and HTLV-1-associated lymphoma occasionally represent a form of intravascular proliferation.