The purpose of this study is to evaluate the possibility of expanding an edentulous ridge spanning two or more teeth by a two-step technique with bioresorbable collagen membranes. Sixteen healthy patients were treated, four in the mandible and 12 in the maxilla. The borderline of the crest width was less than or equal to 4 mm. In each patient only one ridge augmentation was performed. After elevation of a full-thickness flap, a surgical stent was positioned to identify the area of ideal implant positioning. The width of the crest at the location of the surgical stent was measured at the time of GBR procedure and 7 to 12 months later during implant insertion. Native collagen sponges were placed buccally and lingually, and a collagen membrane was shaped and trimmed to completely cover the edentulous ridge. The flaps were sutured to achieve primary closure. Antibiotic and clorhexidine mouthrinse were prescribed, and the patients were recalld every 2 weeks. At implant placement, the mean increase in the size of the crest was 2.49 mm (± 1.61 mm). In 12 out of 16 patients (75%) it was possible to insert 27 implants according to the prosthetic need established previously. All implants were successfully loaded, and in the foru cases where no aprpeciable results were obtained, no clinical complciations or loss of hard and soft tissue were observed.