Purpose: There has been considerable controversy about the placement of barrier membranes over osteotomy and graft sites in sinus bone grafts via the lateral window approach. Particularly when the sinus membrane remains intact, clinicians should consider the benefits and costs of a barrier membrane. This article presents clinical and radiologic findings following repositioning of a detached bony window without a barrier membrane in the lateral approach for maxillary sinus bone grafts. Materials and Methods: After a complete 360-degree osteotomy on the lateral maxillary wall, a bony window was outfractured and separated from the sinus membrane by gentle elevation. After the sinus membrane was confirmed to be intact, grafting was carried out and the bony window was repositioned over the graft material without rigid fixation or a barrier membrane. Clinical and radiologic examinations were performed 6 months postoperative. The relationships between the patterns of gap bone healing, number of implants, time of implant placement (simultaneous with grafting or staged), and thickness of the lateral sinus wall were analyzed. The Fisher exact test and Spearman nonparametric correlation coefficient were employed for statistical evaluation. Results: All 23 included patients experienced no complications. Overall external cortical healing and bone regeneration in the gap between the repositioned window and the lateral wall of the sinus were satisfactory. No significant differences in the patterns of gap bone healing were found, with respect to the number of implants placed or time of implant placement. As the lateral sinus wall was thinner, gap bone healing was better. To date, no implants have failed. Conclusion: A detached bony window that is repositioned on graft material might function as a barrier membrane in the lateral approach for maxillary sinus bone grafts. Schlagwörter: bone grafting, dental implants, maxillary sinus, membranes