The maxillary sinus is one of the most important paranasal sinuses, both from the anatomical and clinical points of view. It is considered to be the keystone structure in most paranasal sinus diseases. Knowledge of the maxillary sinus and its possible anatomic variations are becoming increasingly important to avoid many complications that may occur while conducting a surgical procedure related to the maxillary sinus. The aim of this work was to elucidate the different anatomical variations of the maxillary sinus in the adults by using anatomic and imaging techniques. Also the work aimed at studying the possible relation of these anatomic variations to maxillary sinus diseases. The study was conducted in three sectors: Dry bone study using seventy-one dry maxillae chosen from skulls of persons above age of 23 years, cadaveric study using twenty sagittal sections of adult cadaveric head and neck specimens, CT study using serial coronal and horizontal CT scans for ninety-two persons. The dry bone study revealed the presence of bony septa within the maxillary sinus in 19.7% of cases, dehiscences over the roots of the teeth in 4.2% of cases, supernumerary tooth in 1.4% of cases, and Haller’s cells in 5.6% of cases. The cadaveric study revealed the presence of maxillary sinus hypoplasia in 10% of cases, accessory ostium in 10% of cases, and a septum in 10% of cases. The CT study revealed the presence of maxillary sinus hypoplasia in 17.4% of cases, septa in 16.3% of cases, and Haller’s cells in 13% of cases. These variations were associated with sinusitis in 30.3% of cases.