Purpose: To compare the outcomes of implants inserted in maxillary sinuses augmented with 100% anorganic bovine bone (ABB) grafts versus mixed with 50% ABB and 50% autologous bone graft using a lateral window approach. Materials and methods: This study was designed as a randomised controlled trial of parallel groups. Patients in need of an implant-supported prosthesis in maxillary posterior areas, with a residual alveolar bone height ranging between 0 and 4 mm, were recruited for lateral sinus grafting and implant placement. Patients were randomly allocated to receive two different graft materials according to a parallel group design: group A was grafted with 50% ABB and 50% autogenous bone; group B was grafted with 100% ABB. After 7 months, tapered implants were inserted with an insertion torque between 20 and 45 Ncm. Three months later implants were loaded with screw-retained temporary crowns. Definitive crowns were delivered after 3 months. Outcome measures were implant and prosthesis survival rates, complications, radiographic marginal bone-level changes, probing pocket depths (PPDs) and bleeding on probing (BOP). Clinical data were collected at definitive prosthesis delivery, and 1, 2 and 5 years after definitive loading. Results: Thirty-two consecutive patients were treated with 32 sinus elevation procedures (16 group A, 16 group B). A total of 46 implants were inserted. One patient (with two implants) dropped out in group A, and two patients (with three implants) dropped out in group B. No implant/crown failed by the end of the study. Three complications (one sinus membrane perforation and two chipping of the ceramic) were observed in three patients in group A, versus none in group B (relative risk was 0.81; 95% CI 0.64-1.03; P = 0.225). At the 2-year follow-up, the mean marginal bone loss was 1.18 ± 0.50 mm (95% CI 0.95-1.45 mm) in group A and 1.28 ± 0.48 mm (95% CI 0.97-1.43 mm) in group B, with no statistically significant differences between the two groups (difference 0.11 ± 0.22 mm; 95% CI −0.06-0.16 mm; P = 0.586). At the 5-year follow-up, the mean marginal bone loss was 1.37 ± 0.48 mm (95% CI 1.13-1.86 mm) in group A and 1.42 ± 0.48 mm (95% CI 1.17-1.90 mm) in group B (difference 0.15 ± 0.08 mm; 95% CI 0.10-0.22 mm; P = 0.426). At the 2-year follow-up, the mean PPD value was 2.70 ± 0.39 mm for group A and 2.54 ± 0.66 mm for group B, with no statistically significant difference between groups (difference 0.17 ± 0.39 mm; 95% CI 0.06-0.32 mm; P = 0.456). At the 5-year follow-up, the mean PPD value was 3.20 ± 0.44 mm for group A and 3.32 ± 0.49 mm for group B (difference 0.12 ± 0.43 mm; 95% CI 0.02-0.22 mm; P = 0.672). At the 2-year follow-up, the mean BOP value was 1.21 ± 0.79 for group A and 1.28 ± 0.68 for group B (difference 0.06 ± 0.49; 95% CI −0.23-0.25; P = 0.297), and at the 5-year follow-up, the mean BOP value was 1.77 ± 0.62 for group A and 1.91 ± 0.48 for group B (difference: 0.14 ± 0.51; 95% CI −0.05-0.33; P = 0.492). Conclusions: Within the limitations of this study, the present data confirm similar clinical outcomes of implants inserted in sinuses grafted with ABB versus implants inserted in sinuses grafted with mixed 50% ABB and 50% autologous bone. Keywords: anorganic bovine bone, atrophic maxilla, autologous bone, dental implant, sinus elevation Conflict of interest statement: This study was not supported by any company. All the authors declare no conflict of interest.