Introduction: Autologous bone is considered the reference standard for bone-grafting procedures. A barrier membrane covering an autologous bone graft (guided bone regeneration [GBR]) is expected to prevent graft resorption. Good clinical results have been reported for GBR, although potential complications and relatively high costs have been implicated as disadvantages. However, most studies on the subject have been uncontrolled. Purpose: The aim of this systematic review was to evaluate the available evidence that barrier membranes prevent bone resorption in autologous onlay bone grafts. The primary outcome measure was bone resorption. Results: The search yielded 182 articles. Two observers independently appraised 32 relevant studies methodologically, yielding 14 controlled studies. The articles included human and animal experiments with heterogenous objectives and outcome variables. Although most authors concluded that they had found evidence for the protective effect of barrier membrane on bone resorption in bone grafts, this systematic review reveals that the available evidence is too weak to support this. Most included studies were animal experiments; thus, extrapolation to the human situation is difficult. Most studies also had a small number of test sites, and sample size justification was generally not reported. Furthermore, ambiguity and lack of significance were found in many studies, along with additional limitations such as implantation site, nonsuitable designs, and varying outcome measures. Conclusion: Based on a systematic review of the literature, further evidence is needed to determine whether barrier membranes prevent bone resorption in autologous onlay bone grafts. Schlagwörter: artificial membranes, bone grafts, bone