We analyzed atelectasic processes occurring in the maxillary sinus. Several publications in the literature have tempted to analyze the pathogenesis. Clinically the processes are often silent and only revealed when the major opthalmological complication, enophthalmia, becomes patent. In other cases there is a long history of chronic sinusitis. There is a spectacular retraction of the maxillary sinus walls leading to collapse of the orbital floor and enophthalmia. We report four cases of maxillary sinusitis with atelectasia of the sinus walls at different stages of progression. These observations and data in the literature emphasize the importance, whatever the state of development, of endoscopic osteal decompression to avoid ophthalmological complications.