Purpose: The purpose of this study was to determine the prevalence, size, location, and morphology of maxillary sinus septa in dentate, partially dentate, and edentulous maxillae. Materials and Methods: Data from 312 sinuses were analyzed from reformatted computerized tomograms utilizing SlM/Plant software. The sample consisted of 156 patients (106 women and 50 men, with ages ranging between 24 and 86 years and a mean age of 55.4 years) who were being treatment-planned to receive implantsupported restorations. Results: A total of 75 septa were found in 312 maxillary sinuses (24%), which corresponded to 32.7% of the patients (51 of 156). Completely edentulous patients presented with 33.3% of the total septa, while 66.7% of the septa were identified in partially edentulous patients. Analysis of the anatomic location of the septa within the sinus revealed that 18 (24.0%) septa were located in the anterior region, 31 (41.0%) were in the middle, and 26 (35.0%) were in the posterior region. Measurements of height of the septa varied among different areas. The lateral area ranged from 0 to 15.7 mm (with a mean of 3.54 ± 3.35 mm), the middle area ranged from 0 to 17.3 mm (with a mean of 5.89 ± 3.14 mm), and the medial area ranged from 0 to 20.6 mm (with a mean of 7.59 ± 3.76 mm). A total of 20 septa (26.7%) were located in the immediate apical region of teeth. The remaining 55 septa (73.3%) were related to edentulous areas. Discussion: Septa may arise in any of the 3 regions of the maxillary sinus irrespective of the degree of dentulism or edentulism present. Conclusion: To avoid unnecessary complications during sinus augmentation procedures, adequate and timely identification of the anatomic structures inherent to the maxillary sinus are required.