Background: Maxillary sinus is pyramidal cavity located in the body of maxilla; represent the largest and closest paranasal sinus to oral cavity. Maxillary sinus shape, size and volume affected by any developmental disturbance occur in midfacial area such as cleft lip and palate. The aim of this study is to evaluate maxillary sinus volume in cleft lip/palate patients and compare it to control normal subjects by using Cone Beam Computed Tomography. Material and method: Thirty four Cone Beam Computed Tomography images (17 of cleft patients and 17 controls) were collected, and Maxillary sinus volume was measured in cleft patients (cleft side and non-cleft sidd), and control group (right and left side).Comparison between study groups and statistical analysis was done. Results: the mean of sinus volume in cleft side was 7.76±2.4 mm 3 , in non-cleft side was 9.03±2.2 mm 3 , and in control group(mean of right and left side) was 11.34±2.8 mm 3 .maxillary sinus volume of cleft side was smaller than non-cleft side with no statistical significant difference. But there was high significant difference when compared to control group P= 0.0009. Conclusion:cleft lip and palate affect the normal development of maxillary sinus in cleft side. knowledge about maxillary sinus anatomy and volume is important point for surgeon required in sinus surgery, implant placement and any treatment of craniofacial disease.