Chronic maxillary atelectasis (CMA) and silent sinus syndrome (SSS) are rare clinical entities characterized by an implosion of the maxillary sinus that may or may not be associated with sinonasal symptoms, and are complicated by ipsilateral enophthalmos. The objective of this article is to discuss the definitions, physiopathology, clinical and radiographic characteristics, and surgical management of these entities. We retrospectively reviewed 18 patients (7 women, 11 men, aged 12-70 years) diagnosed and treated in the ear, nose, and throat departments of four Belgian teaching hospitals between 2000 and 2015. Nine patients had a history of sinus disease. In all cases, a computed tomography scan showed downward displacement of the orbital floor, increased orbital volume, and maxillary sinus contraction. Five patients met the criteria for grade II CMA and 13 for grade III CMA. Four patients met the criteria for SSS. All patients underwent wide endoscopic middle maxillary antrostomy. There were no orbital complications and all patients experienced resolution or a dramatic reduction of their symptomatology. Only one patient asked for an orbital floor reconstruction to correct a persisting cosmetic deformity. Although CMA and SSS are usually regarded as different entities in the literature, we believe that they lie on the same clinical spectrum. Treatment for both conditions is similar, i.e., middle meatal antrostomy to halt or even reverse the pathological evolution and reconstruction of the orbital floor in the event of persistent cosmetic deformity.