Background: Autologous growth factors are currently evaluated for their potential to enhance bone formation in association with maxillary sinus floor augmentation (MSFA). Aim/Hypothesis: To evaluate histologically whether chair-side prepared autologous platelet rich growth factor (PRGF) in combination with deproteinized bovine bone (DBB) enhances bone formation when compared with DBB alone as graft material in MSFA. Material and methods: Six partially edentulous patients with ≤3 mm residual bone height bilaterally in the posterior maxilla were subjected to MSFA with DBB in combination with PRGF in one side or DBB alone in the contralateral side. PRGF was prepared by collecting 20 ml of peripheral blood from each patient into tubes containing 3.8% (wt/vol) sodium citrate as anticoagulant and centrifugation at 1400 rpm for 8 min at room temperature (PRGF System1, Vitoria, Spain). From the separated blood, the 0.5 ml plasma fraction located just above the red cell fraction, but not including the buffy coat, was then collected and deposited in an eppendorf tube, and activated with the addition of PRGF activator (50 ll calcium chloride solution 10%w/v). The resulting PRGF was then mixed with deproteinized bovine bone (DBB) in a glass dish. After 5–8 min, the material attained a viscous consistency and was ready for application. MSFA was performed with the lateral window technique. Trephine biopsies were obtained during oral implant site preparation approximately 6 months after MSFA and processed for decalcified or non-decalcified histological and histomorphometrical evaluation. Non-parametric statistics, with P set at 0.05, were performed. Results: The collected biopsies varied in length (range: 3.5– 9.9 mm); consequently, the portion of the biopsy representing augmented tissues also varied (range 2.3–14.6 mm2). New bone formation with a trabecular appearance and numerous DBB particles in contact with the new bone or with loose connective tissue were observed. No differences in the relative volumes of bone formation were found in sinuses augmented with DBB+PRGF or DBB alone 6 months after MSFA (35.6 8.26 mm and 37.8 3.15 mm, respectively). Conclusions and clinical implications: Based on these preliminary results, PRGF as an adjunct to DBB does not enhance bone formation inside the human sinus when implant installation is planned several months after MSFA.