Purpose: The purpose of this study was to evaluate changes in alveolar bone height after direct sinus elevation and simultaneous implant placement in the posterior edentulous maxilla. Materials and Methods: A prospective clinical study was conducted of patients undergoing sinus elevation for implant placement in the posterior maxilla to replace missing teeth. Residual alveolar bone height was between 4 and 7.5 mm. Lateral osteotomy of the maxillary sinus, followed by simultaneous implant placement without bone grafting, was performed under local anesthesia. Prosthetic restoration was completed 9 months later. The changes in alveolar bone height at the sinus floor were assessed radiographically after 1 week and 6, 9, 18, and 28 months after implant placement. Probing depths, implant mobility, and crestal bone loss were assessed at the same intervals. Results: Twenty-eight patients (17 women and 11 men) participated in the study. Forty-five implants were placed and followed after prosthetic rehabilitation. At 18 months after loading of the implants, alveolar bone height in the area of sinus elevation ranged from 7.40 to 11.55 mm. Increases in alveolar bone height at the sinus floor ranged from 2.05 to 5.40 mm at a minimum of 18 months after loading, a statistically significant gain. Crestal bone loss and changes in probing depths were not significant in any patients, and all implants remained clinically stable. The implant success rate was 100% without any complications after 18 to 28 months of follow-up. Conclusion: Placement of endosseous implants in the atrophic posterior maxilla in conjunction with sinus elevation without bone grafting resulted in a significant amount of bone formation around the implants at the sinus floor, resulting in successful restorations and eliminating the need for bone grafting.