Purpose: The objective of this 3-year post-loading parallel randomised controlled trial is to compare two bone substitutes and resorbable membranes in a one-stage procedure for horizontal bone augmentation: anorganic bovine bone and porcine collagen membranes (BB group) versus synthetic resorbable bone graft substitute made of pure β-tricalcium phosphate and porcine pericardium collagen membranes (CJ group). Materials and methods: Patients in need of implant treatment having at least one site with horizontal osseous defect at a private clinic in Rimini, Italy, were included in this study. Patients were randomised to receive either BB or CJ in a one-stage procedure for horizontal bone augmentation in a submerged approach. Randomisation was computer-generated with allocation concealment by opaque sequentially numbered sealed envelopes. Patients and the outcome assessor were blinded to group assignment. The abutment connection was made after 6 months of healing. The application of the provisional prosthesis was performed after abutment connection and a definitive metal-ceramic prosthesis was placed 6 months post-loading. The patients were followed-up to 3 years post-loading. Primary outcome measures were: implant failure, complications and peri-implant margin bone level changes. Secondary outcome measures were: visual analogue scale (VAS) for functional and aesthetic satisfaction and pink aesthetic score (PES). Results: Twenty-five patients with 32 implants were randomly allocated to the BB group and 25 patients with 29 implants to the CJ group. All 50 randomised patients received the treatment as allocated and there were 7 drop-outs in the BB group and 11 drop-outs in the CJ group up to 3 years' post-loading. There were no implant failures. There were six complications in five patients of the BB group and three complications in three patients of the CJ group (relative risk: 1.32, 95% CI from 0.37 to 4.64, P = 1.0000). Radiographic bone loss was 1.61 mm for the BB group and 1.02 mm for the CJ group (difference 0.54 mm, 95% CI from -0.53 to 1.60, P = 0.3100). The functional VAS was 9.0 for the BB group and 9.6 for the CJ group (difference 0.6, 95% CI from -0.4 to 1.5, P = 0.2393). The aesthetic VAS was 9.4 for the BB group and 9.6 for the CJ group (difference 0.2, 95% CI from -0.5 to 0.8, P = 0.6141). PES was 8.7 for the BB group and 8.5 for the CJ group (difference -0.1, 95% CI from -2.9 to 2.7, P = 0.9360). Conclusions: No significant differences were observed in this randomised controlled trial comparing anorganic bovine bone with porcine collagen membranes versus synthetic resorbable bone made of pure β-tricalcium phosphate with pericardium collagen membranes for horizontal augmentation. Keywords: bone dehiscence, bone substitutes, dental implant, guided bone regeneration, horizontal bone augmentation, randomised controlled trial Thommen Medical AG provided the implants as well as the Jason membrane and Ceros TCP free of charge.