Chronic maxillary atelectasis (CMA) results from valvular occlusion of the natural ostium of the maxillary sinus by the medial infundibular wall. This uncommon condition is characterized by a chronic decrease in sinus volume caused by inward bowing of one or more antral walls. In some instances, visual and cosmetic problems can occur as a consequence of severe osseous wall deformation. CMA is seen in both children and adults, and radiological evidence of complete antral opacification and fontanel retraction is considered diagnostic of the disorder in both populations. Treatment goals are the same for all age groups and include complete antral drainage and restoration of good ventilation.