Purpose: To compare the outcome of implants inserted in maxillary sinuses augmented with anorganic bovine bone (ABB) grafts vs mixed 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 a maxillary posterior area with a residual alveolar bone height no greater than 4 mm (range 0-4 mm) were recruited for lateral sinus grafting. Patients were randomly allocated to receive 50% ABB and 50% autogenous bone (group A) or 100% ABB (group B). After 7 months, tapered implants were inserted with an insertion torque between 20 and 45 Ncm. After 3 months, implants were loaded with screw-retained temporary crowns. Definitive crowns were delivered 3 months later. Outcome measures were implant survival, complications, radiographic marginal bone-level changes, probing pocket depths (PPD) and bleeding on probing (BOP). Clinical data were collected at definitive prosthesis delivery, 1 and 2 years after loading. Results: Thirty-two consecutive patients were treated with 32 sinus lift procedures (16 group A, 16 group B). A total of 46 implants were installed. No patient dropped out. No crown/implant 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, vs none in group B (RR 0.81; 95% CI 0.64 - 1.03 mm; P = 0.225). At the 2-year after final loading 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 same follow-up, the mean PPD value was 2.70 ± 0.39 for group A and 2.54 ± 0.66 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), while 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 mm; 95% CI -0.23 - 0.25 mm; P = 0.297). Conclusions: Within the limitations of this study, the present data seem to confirm the hypothesis that the clinical outcome of implants inserted in sinuses grafted with ABB vs implants inserted in sinuses grafted with mixed 50% ABB and 50% autologous bone are comparable. Keywords: anorganic bovine bone, atrophic maxilla, autologous bone, dental implants, sinus lift Conflict-of-interest statement: This study was not supported by any company. All the authors declare no conflict of interest.