Objectives: This study was designed to clarify the changes that might be induced in the maxillary sinus walls thickness in response to TMJ bony ankylosis. Subjects and methods: Forty five (45) subjects were included in the study. They were divided into two groups Group I, (patients group) comprised fifteen 15 patients were suffering from temporomandibular joint bony ankylosis (26 maxillary sinuses involved) and Group II, (control group) contained thirty (30) healthy volunteer. Maxillary sinus walls thickness has been measured by computerized tomography scan for both groups and was compared. Results: There was significant increase in mean thickness of all walls of maxillary sinus in patients group. The thickness of lateral wall of recurrent cases of TMJ ankylosis showed significant decrease when compared with the non-recurrent cases. Conclusion: Observable increase in the thickness of maxillary sinus walls. This may be attributed to bone apposition from outer side without resorption from inner side. This explanation is ascribed to lack of pneumatization associated with hindrance of upper air way that usually existing with cases of TMJ bony ankylosis.