Purpose: Scientific publications have recently found that bone graft quality and implant survival rates were not influenced by antrostomy membrane coverage during maxillary sinus floor augmentation with a lateral approach. The aim of this study was to evaluate the stability of the bone substitute after a maxillary sinus floor augmentation procedure with or without using a covering membrane. Materials and Methods: This retrospective study evaluated all patients who were enrolled between April 2016 and January 2017. The stability of the bone graft inside the sinus cavity and at the level of the lateral bone window was assessed through preoperative and postoperative cone beam computed tomography images up to 6-month follow-up. The clinical postoperative morbidity was evaluated following a visual analog scale protocol. Results: Maxillary sinus floor augmentation with a lateral approach was performed in 41 patients. In 17 cases (10 women/7 men, mean age: 55.4 years), a barrier membrane was used to cover the lateral bone window (control group), and in 24 cases (13 women/11 men, mean age: 56.2 years), no membrane was used (test group). The bone graft dislodgment within the buccal mucosa at 6 months postoperative ranged from 0 to 12.2 mm (mean ± SD value: 3.8 ± 3.1 mm) in the test group and from 0 to 2.3 mm (mean ± SD value: 0.5 ± 0.4 mm) in the control group. The postoperative pain and swelling complications were significantly more important for the test group (3.3 ± 1.4/4.3 ± 4.5, respectively) than for the control group (2.1 ± 0.9/2.7 ± 0.9). Conclusion: On the basis of this preliminary study, it appears that the use of a barrier membrane to cover the lateral bone window during maxillary sinus floor augmentation surgery with a lateral approach reduces the postoperative dislodgment of the bone graft throughout the sinus antrostomy and prevents the bone substitute particles from penetrating within the buccal mucosa, which is related to postoperative morbidity. Schlagwörter: barrier membranes, bone substitutes, computed tomography, sinus floor elevation, sinus membrane