Aim: The purpose of this study was to investigate the potential of the local administration of organic silicon on autogenous grafted critical-sized cortical bone defects. Material and Method: Twenty-four rats were divided into three groups: group C (passive control), group Au, and group Si. A 5-mm diameter critical-size defect was created in the calvarium of each rat. In group C, only a sterile saline-treated absorbable collagen sponge was applied to the defect area. In group Au, autogenous graft was performed and sterile saline-treated absorbable collagen sponge was applied on the autografted defect area. In group Si, autogenous graft was performed and a 500 mg silicon-treated absorbable collagen sponge was applied to the autografted defect area. All animals were euthanized at 28 days postoperative. Stereologic analyses were performed. New bone area and connective tissue volumes were measured. Results: Stereologic analysis showed that the difference between group Si with a mean bone formation of 1.79 +/- 0.48 mm3 and groups Au and C was statistically significant (p <= 0.05), the latter having mean bone formations of 1.50 +/- 0.51 mm3 and 1.04 +/- 0.03 mm3 respectively (p <= 0.05). Connective tissue volume was larger in group Au than in group Si, but the difference was not statistically significant. Discussion: Locally administered organic silicon enhances bone regeneration in critical-size calvarial rat defects filled with autogenous graft.