Purpose: It was the aim of the present prospective study to quantify the gain in height of implant sites by endoscopically controlled osteotome sinus floor elevations (ECOSFE) with simultaneous implant placement and to report the number of sinus membrane perforations. Materials and Methods: From October 1999 to December 2000, of 92 sinus floor elevations, 18 were carried out endoscopically controlled with an osteotome technique. As augmentation material, -tricalcium phosphate (-TCP) or autogenous bone was used; 22 implants were placed. Results: The residual height of the alveolar crest in the posterior maxilla was 6.8 ± 1.6 mm on average. The implant lengths ranged from 10 to 16 mm (mean implant length 12.2 ± 1.4 mm). They were significantly larger than the residual height of the alveolar crests (P .0005). Elevation of the sinus floor with an osteotome had to be supported by conventional sinus floor elevation instruments after a mean elevation of 3.0 ± 0.8 mm to prevent perforation of the sinus membrane. However, 1 perforation occurred, which was repaired with a periosteal patch. At stage 2 surgery, 2 implants were removed because of mobility. Endoscopic control revealed one case in which -TCP could be found within the sinus; another case showed areas of polypoid mucosa on the sinus floor. Discussion: With the ECOSFE, perforations of the sinus membrane can be visualized; however, they cannot be avoided. Although this technique is less invasive than the lateral window technique, it cannot be recommended as a standard procedure in the posterior maxilla because of the large amount of additional equipment needed and the technically demanding procedure. Conclusion: The use of the ECOSFE should be confined to scientific trials.