Purpose: This retrospective study was designed to evaluate the volume of hard tissue generated at the time of implant placement in distracted alveolar bone. Materials and Methods: All patients who underwent distraction osteogenesis between 2000 and 2003 were included. The preoperative bone height, amount of distraction performed, and presence or absence of complications affecting implant placement were recorded. The augmentation achieved was correlated with insufficient bone formation using the Spearman correlation and the Fisher exact test. Results: The study included 43 implants placed in 17 cases of alveolar distraction. Of the 34 implants placed in bone augmented by 4.5 to 6.5 mm, bone defects were observed with 12. All 9 implants placed in ridges augmented by 7 to 10.5 mm demonstrated a bone defect. The ¡°defect¡± and ¡°no-defect¡± implant groups differed significantly with respect to preoperative bone height and amount of distraction performed (P .001 for both). Significantly more defects were formed in bone augmented by > 25% compared to bone augmented by ¡Ü 25% (P .001). Conclusions: When considering distraction osteogenesis, augmentation of up to 25% of the initial bone height seems more predictable and less likely to be associated with complications at the time of implant placement. In distractions greater than 25% of the original height, additional treatment should be considered. Keywords: alveolar distraction, bone regeneration, dental implants, distraction