Purpose: Osteotome sinus floor elevation (OSFE) is a technique aimed at simplifying implant placement in the posterior atrophic maxilla. The necessity of bone grafting under the elevated sinus membrane has been widely debated. The aim was to compare the evolution over 5 years of implant stability in sites grafted or left ungrafted. Materials and methods: A total of 12 patients (9 female and 3 male) presenting ≤ 4 mm initial bone height (IBH) in the posterior maxillary sites were recruited. Implants (n = 37) were placed using OSFE. According to the randomisation, the sinuses received either bone graft (n = 20, control group) or no graft (n = 17, test group). Patients received both these treatments when both sinuses fulfilled the inclusion criteria. Control assessments were performed 1 week, 10 weeks, 12 weeks, and then 1 year, 3 years and 5 years after the implant placement. Periapical radiographs were taken and the implant stability quotient (ISQ) was measured at different time points. Results: At implant surgery, the mean ISQ was 58.9 ± 11.2 for the test group and 53.8 ± 10.2 for the control group; it plummeted 10 weeks after the implant placement and rose thereafter. Five years after the implant placement, the mean ISQ reached 80.8 ± 4.2 for the control group, and 79.7 ± 4.3 for the test group. The difference between the groups was not significant. The IBH significantly affected implant stability at implant insertion and 5 years after the implant insertion, but not at the other time points. Conclusions: The implants performed using OSFE in ungrafted sites were as stable as the implants placed in grafted sites. Keywords: bone graft, implant stability quotient (ISQ), osteotome sinus floor elevation (OSFE), posterior maxilla, resonance frequency analysis (RFA) Conflict of interest statement: All authors report no conflict of interest.