Purpose: The aim of this randomised, controlled, parallel-group clinical trial was to evaluate the clinical effect of platelet-rich plasma (PRP) on bone graft healing and implant integration in iliac crest grafted maxillae. Materials and methods: Twenty-two consenting patients were randomised to PRP (13 patients) and control (9 patients) groups. Both groups received onlays and 16 patients had their maxillary sinus grafted with particulate bone (lateral window approach) with iliac crest bone grafts. Autologous platelet concentrates were prepared from the patients' blood and autologous thrombin was produced. PRP was mixed with the test group bone grafts. Outcome measures were implant integration, implant stability, soft tissue healing, graft resorption, and donor and recipient site complications. Implant stability measurements were recorded at placement and exposure using a resonance frequency analysis device. Patients were followed up to abutment connection. Multiple linear regression analyses using robust standard error were performed, taking the patient as the unit of measurement. The t test was also used where appropriate. Results: One bone graft failed in the PRP group and regrafting was required. No statistically significant differences were observed for soft tissue healing indices (P = 0.4) and mean graft resorption (P = 0.5) between groups. All implants were found clinically integrated at time of exposure. No statistically significant differences in implant stability were observed between groups at implant placement (P = 0.059) and exposure (P = 0.1). Using a post-hoc analysis, posterior implants in the PRP group showed statistically significantly higher stability values (61 ± 2.6) than anterior implants (60 ± 2.4) at implant placement (mean difference -0.95, P = 0.04). However, this difference was not clinically significant. Conclusion: No appreciable clinical effect could be observed when using PRP with autologous iliac crest bone graft in the maxilla. Schlagwörter: bone graft, iliac crest, implant stability, maxilla, platelet-rich plasma Conflict-of-interest statement: There is no financial conflict of interest.