Purpose: To present a sling suture technique used to stabilize a collagen membrane against the lateral bone window to improve bone substitute stability inside the sinus cavity. Materials and Methods: Maxillary sinus floor augmentation was performed on 17 patients (8 women and 9 men; mean age 58.2 years) using a lateral approach with the sling suture technique to maintain a collagen membrane against the lateral bone window. Postoperative CBCT images were captured at 6-month follow-up of each patient to monitor the bone graft stability at the level of the lateral antrostomy. Clinical postoperative pain and swelling were assessed via visual analog scale (VAS) questionnaire, measured from level 1 (low) to level 5 (acceptable) to level 10 (high) at 1 week postoperative. Results: No bone substitute displacement was observed in any clinical cases on the CBCT images at 6 months postoperative. The pain and swelling levels observed 1 week postoperatively were significantly low (mean ± SD; 1.6 ± 1.0 and 2.1 ± 0.9, respectively). Conclusions: The use of the sling suture technique to maintain a barrier membrane at the level of the lateral bone window in cases of maxillary sinus floor augmentation using a lateral approach is a predictable protocol to prevent bone substitute displacement outside the sinus cavity.