Objectives: Sinus augmentation with a lateral window approach is the traditional treatment when the atrophic posterior maxilla's residual bone height (RBH) is ≤6mm. The goal of the current research is to compare the clinical and radiographic results of the transcrestal approach in sites with RBH ≤6mm compared to the lateral window approach. Subjects and Methods: Twenty-two patients with one or more extracted teeth in the sinus zone of the posterior maxilla and a subantral RBH of ≤6mm were selected for the study. Their ages varied from 34 to 59. At random, two equal groups of patients originated: group (I) received dental implants following a sinus lift utilizing the lateral window approach, while group (II) included patients who underwent dental implantation after a sinus lift through a transcrestal approach. All patients were clinically evaluated at the following intervals: preoperative, immediate, one, three, and six months postoperatively. Sinus membrane perforation, pain, edema, and implant stability were clinically evaluated. Radiographic assessment using CBCT was used to measure the ridge height and bone density. Results: The incidence of intraoperative sinus membrane perforation, postoperative pain, and swelling in the transcrestal approach group was lower than that in the lateral approach group. All implants had primary stability with significant improvement in secondary stability measured 6 months postoperatively in both groups. Conclusions: The transcrestal approach can be considered an effective and safe alternative to the lateral window approach in the atrophic posterior maxilla.