Purpose: The purpose of this retrospective study was to compare a bidirectional distraction system with a unidirectional system with regard to bone height attained and the need for secondary graft procedures. Materials and Methods: Unidirectional and bidirectional distractor devices were used for vertical augmentation of the maxilla and mandible in 2 separate groups of patients (n = 10 and n = 11, respectively). Clinical and radiographic outcome data were collected at postoperative follow-up examinations for up to 2.5 years. The height of the augmented alveolar ridge and the sagittal location of the bone fragment were measured on panoramic radiographs or lateral cephalograms. These data were analyzed with 1-way analysis of variance. Nonparametric data, such as treatment complications, were analyzed with the Fisher exact test. The dental implant survival data were evaluated with a Kaplan-Meier survival analysis. Results: The difference in vertical bone gain observed between unidirectional and bidirectional groups (5.3 plusmn 1.8 mm vs 6.1 plusmn 2.3 mm) was not statistically significant. In the unidirectional group, additional autogenous bone grafting was required in 6 cases, while grafting was required in only 2 cases in the bidirectional group. This difference was due to the more precise control of the distraction process associated with the bidirectional distractor; however, it was not a statistically significant difference. Postaugmentation, 59 implants were placed in the augmented sites. These implants exhibited primary stability and were restored with good functional and esthetic results. Conclusions: The need for additional grafting procedures may be reduced in cases where the distraction vector is optimized, as generally seen with bidirectional distractor use. Schlagwörter: augmentation, bidirectional distraction, complications, dental implants, distraction osteogenesis