Objectives: To evaluate whether the adjunctive use of a bone substitute at immediate single implants placed in fresh extraction sockets with a residual buccal bone-to-implant gap of at least 1 mm could improve the aesthetic outcome of guided bone regeneration (GBR). Materials and methods: Eighty patients requiring bone augmentation at a single immediate postextractive implant to improve the aesthetic outcome were randomly allocated to an augmentation procedure using a resorbable barrier alone (GBR group; 40 patients) or a bone substitute plus a resorbable barrier (GBR + BS group; 40 patients) according to a parallel group design at four different centres. Three to 4 months after implant placement/augmentation, implants were loaded with provisional or definitive single crowns. Outcome measures were implant failures, complications, aesthetics assessed using the pink esthetic score (PES), patient satisfaction and peri-implant marginal bone levels, recorded by blinded assessors. All patients were followed up to 1 year after loading. Results: One patient dropped out from the GBR group. Seven (9%) implants failed: 2 (5%) in the GBR + BS group and 5 (12.5%) in the GBR group. Six minor complications occurred in the GBR + BS group versus 2 in the GBR group. These differences were not statistically significant. Just after implant placement/augmentation, mean bone levels were -0.21 mm at GBR + BS implants and -1.92 mm at GBR implants whereas at 1 year after loading they were -1.04 and -1.76, respectively. When comparing the two groups, GBR + BS implants had 0.70 mm more peri-implant marginal bone than GBR implants. Aesthetics was scored by a blinded assessor as statistically significantly better for the GBR + BS group. Patients were equally satisfied. There were no differences between centres regarding the clinical outcomes. Conclusions: The use of additional anorganic bovine bone substitute (Endobon) with resorbable collagen barriers (OsseoGuard) in defects around post-extractive implant improves the aesthetic outcome, though single post-extractive implants might be at a higher risk for implant failures. Keywords: guided bone regeneration, post-extractive implants