Relapse after allogeneic bone marrow transplantation (BMT) usually occurs in the bone marrow and is often associated with a poor prognosis. Isolated extra-medullary relapse following BMT is exceedingly rare. We observed an isolated relapse in the left retro-orbital region of a 13-year-old girl, 3 years after BMT performed for acute lymphoblastic leukaemia in third complete remission. Computerized tomography revealed a tumor at the inferomedial part of the orbit infiltrating the maxillary and ethmoid sinuses and nasal cavities and also involving the rectus muscles. Histology demonstrated a monomorphic leukaemic infiltrate. Complete disappearance of the retro-orbital mass was obtained with chemotherapy and local irradiation.