Aneurysmal bone cysts is a benign, slow growing expansile lesion usually found in long bones or vertebrae. Only 5 cases of ABC of the ethmoid bone have been reported in the literature. Plain radiographs are not specific. CT and MRI are very useful to depict the extent of the lesion and demonstrate the presence of blood-fluid levels, which is a characteristic finding of ABC. We present one atypical case of ABC of the ethmoid bone in a 15-year-old female characterised by its extensive involvement and its rare location.