Purpose: Short implants are an alternative to bone augmentation procedures for patients with reduced bone height. This study evaluated the success of short implants in posterior locations prior to loading. Materials and Methods: Eighteen patients received at least four Astra Tech implants in symmetric posterior locations. Implants (n = 82) ranged from 6 to 11 mm with 70 implants = 9 mm and 38 implants = 6 mm. Placement was planned virtually using software and cone beam computed tomography (CBCT) scans. Computer-generated guides were ordered for all patients; however, lack of interarch distance precluded their use for five patients. In these situations, guides were used to communicate pilot drill position only. Osteotomies were prepared using the guides and accompanying drill sequence following a two-stage surgical approach. Degree of bone mineralization (DBM) parameters for implant osteotomy sites were measured using three-dimensional CBCT images taken before and after implant placement. A paired t test was performed to compare the DBM parameters between failed and successful implantation sites. Results: Early failure occurred for 7 out of 82 implants or 8.5%. All of the failed implants were 6 mm in length and placed using computer-aided design/ computer-assisted manufacture (CAD/CAM) surgical guides. Three failures occurred in one patient. Bone grafting was done for failed implant sites, and after healing, new implants were placed using conventional surgical guides. No further failures occurred. The most frequent value (peak) for DBM was significantly higher for failed implant sites than for successful ones (paired t test, P = .043). Conclusion: Current failures suggest that CAD/CAM guides used with external irrigation may pose a greater risk for the success of 6-mm implants placed in posterior areas with advanced bone loss. This may be due to the bone density in these highly resorbed areas combined with limited irrigation reaching the osteotomy sites. Keywords: short implants, failure, bone density