Purpose: Sinus membrane thickness has been associated with the incidence of membrane perforation during the sinus elevation procedure. Understanding the sinus membrane thickness is essential for prevention of this specific surgical complication. Therefore, the aim of this retrospective study was to investigate the impact of sex, age, and season on the membrane thickness. Materials and Methods: The charts of 144 healthy patients were included in the study. Cone beam computed tomography (CBCT) images from these patients were analyzed to determine the sinus membrane thickness in the coronal and sagittal views. Sex, age, and season were correlated with the membrane thickness. Results: The mean thickness of the sinus membrane was 1.81 ± 1.66 mm (range: 0.47 to 9.49 mm). In 22.12% of the CBCT images, the sinus membrane was not visible. Membrane thickness of less than 2 mm was found in 70.8% of the cases. Age was found to be strongly correlated (P .05) with sinus membrane thickness but not sex or season. Conclusion: Based on CBCT assessment, age was found to be a factor influencing sinus membrane thickness but not sex or season. Schlagwörter: maxillary sinus, nasal mucosa, sinus floor augmentation