We describe a rare case of sinonasal T-cell lymphoma in an 11-year-old boy who presented with a right acute orbit characterized by proptosis, eyelid edema and erythema, limitation of eye movements, and excruciating pain on the right side of his face. Orbital computed tomography showed progressive right extraocular muscle enlargement. One biopsy specimen showed extensive tissue necrosis and an infiltrate of atypical cells with pleomorphic nuclei within the walls of blood vessels. Immunohistochemical studies demonstrated that these cells were positive for leucocyte common antigen (CD45), CD3 cytoplasmic, CD45RO, and terminal deoxynucleotidyl transferase and negative for CD20, CD57, CD56, CD99 and Epstein-Barr virus. Chemotherapy for T-cell non-Hodgkin lymphoma was initiated, but the patient's status deteriorated and the child died of respiratory insufficiency, sepsis, and central nervous system infection.