The silent sinus syndrome (SSS) is a rare clinical entity characterized by painless spontaneous enophthalmos, hypoglobus, and facial deformities secondary to chronic maxillary sinus atelectasis. The aim of this study was to present an SSS diagnostic feature and evaluate the relationship between nasal septum deviation and maxillary sinus volume. A retrospective chart review of the clinical characteristics of 20 patients diagnosed with SSS between January 2013 and July 2014 were analyzed by the Department of Otorhinolaryngology of University Hospital Complex of Santiago de Compostela. 14 patients were females and six males. The mean age was 43 years (range 28-67 years). The right maxillary sinus was involved in 12 patients and the left maxillary sinus in eight patients. There was no statistical difference between gender and the presence of SSS. Maxillary sinus sizes were significantly smaller on the same side as the deviation (p < 0.01). 14 patients were treated with functional endoscopic sinus surgery (FESS) with maxillary antrostomy. We concluded that patients with SSS usually present with facial asymmetry, and the best approach to document and show all facial asymmetries for these patients are the frontal and craneo-caudal photographs. The present study demonstrates that, in adult patients, SSS generally presents a septal deviation to the affected maxillary sinus. We recommend performing a paranasal sinus CT scan when the patient has a deviated nasal septum, retraction of the malar eminence (evidenced from the viewpoint cranio-caudal facial) and hypoglobus. FESS performing postero-anterior uncinectomy and enlargement of the maxillary ostium is recommended to restore sinus pressure and prevent progression of the enophthalmos, hypoglobus and facial deformities.