Purpose: Sinus elevation through the crestal approach has become a routine procedure for implant placement in the posterior edentulous maxilla. The combination of flapless surgery and crestal sinus elevation with simultaneous placement of implants is an attractive surgical approach for implant grafting in the posterior maxilla, but its efficacy and safety have seldom been studied. The aim of this study is to evaluate retrospectively the outcomes of flapless crestal sinus floor elevation using piezosurgery and a hydraulic sinus elevation system with simultaneous implant placement. Materials and Methods: Between October 2009 and August 2010, flapless implant surgery using a crestal approach, accompanied by simultaneous hydraulic sinus elevation and grafting, was performed. Patients were followed up clinically and with intraoral and panoramic radiographs. Any postoperative complications, including swelling, discomfort, infection, fractures, and implant loss, were recorded, and sinus bone gain was measured. Results: Thirty-one sinuses were elevated and 35 implants were placed. Patients were a mean of 41.2 ± 6.69 years old, and 45% were women. The sinus was elevated to 7 to 15 mm, and no membrane perforations were noted. The mean follow-up period was 21 weeks. The mean bone gain under the maxillary sinus was 12.03 ± 2.1 mm, and all implants displayed primary stability with a mean insertion torque >= 15 Ncm. No postoperative discomfort, swelling, hematoma, infection, or bone fenestration was noted. One patient experienced prolonged edema in the lower eyelid region, and another lost an implant. Conclusion: In this retrospective analysis, flapless crestal sinus floor elevation was safe and effective, decreasing surgical discomfort and trauma and early implant failures. Keywords: crestal approach, flapless dental implant placement, hydraulic sinus elevation, piezosurgery, posterior maxillary implant