Purpose: To provide a detailed presentation of computer-aided design/computer-assisted manufacture guidance in severely resorbed posterior maxillae to place implants in a very limited amount of bone, thus avoiding sinus grafting. Materials and Methods: Based on computerized tomography (CT) axial images, implant positions are planned using imaging software. A surgical template is fabricated and drilled with a numerically controlled machine to transfer the planned positions to bone with high accuracy. To avoid sinus grafting, implants can be planned in the anterior or posterior wall and in the septa of the sinus as well as in the palatal curvature. Recipient site preparation is done transgingivally with a drill or with a dedicated bone spreader to increase the amount of bone when necessary. Results: Fifteen resorbed posterior maxillae were treated with a fixed prosthesis supported by a combination of 42 upright and tilted implants. In all cases, implants were placed as planned. Seventeen implants were tilted at a 20- to 35-degree angle with the line perpendicular to the axial CT images. Seven implants were placed in the palatal curvature, 11 implants were close to the anterior wall, and two of them in combination with the palatal curvature. Only one implant was placed close to the posterior wall and two were placed in septa. All patients attended scheduled follow-up visits. During the 4-year observation period, no complications were recorded, no implants were lost, and there was no infection or inflammation. Conclusion: This proof-of-concept study suggests that the use of an image-guided system associated with bone spreading for oral implant placement in the atrophic posterior maxilla can be an alternative to sinus grafting. Keywords: atrophic maxilla, bone graft, bone spreading, computer-aided surgery, implant dentistry, maxillary sinus, minimally invasive surgery, surgical flap, tilted implants, x-ray computerized tomography