Silent Sinus Syndrome is defined as a painless spontaneous and progressive enophthalmos and hypoglobus with maxillary sinus hypoplasia and orbital floor resorption. It is caused by maxillary sinus atelectasis in a setting of ipsilateral chronic maxillary sinus hypoventilation. The syndrome was first described in 1964 by Montgomery, but the term "Silent Sinus Syndrome" was not coined until 1994 by Soparkar. The aetiology is still controversial: some authors postulate a basal hypoplastic sinus, other suggest an acquired process due to an obstruction of the ostium in the medium meatus. Silent Sinus Syndrome presents in the third to fifth decades of life, very rarely in childhood with no gender predilection and it is usually a unilateral disorder. The symptoms are not shown to be related to chronic sinuses disease. The clinical signs are: enophthalmos, hypoglobus, upper lid retraction secondary to dystopia of the globe, sinking of the eye and orbital asymmetry, deepened upper lid sulcus, disappearance of the palpebral fold line, lagophthalmos, vertical diplopia, malar depression, and facial asymmetry. Extraocular muscle function is generally preserved and usually there is no visual impairment. The diagnosis is confirmed by computed tomography scan of the orbits and paranasal sinuses. The treatment consists of orbital reconstruction and functional rehabilitation of the maxillary sinuses.