Fibrous dysplasia is a benign disorder of fibro-osseous tissue of unknown etiology that characteristically manifests itself in children and becomes dormant in early adult life. Depending on whether one or more bones are affected, monostotic and polyostotic forms are defined. The authors are recently experienced a case of monostotic fibrous dysplasia arise in the ethmoidal labyrinth which is confirmed as pathologically. This case report documents the fact that fibrous dysplasia may arise in the ethmoidal labyrinth.