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Management of anterior skull base defects is an area of continued innovation for skull base surgeons. Various grafting materials have been advocated for the repair of skull base defects depending on needs, availability, harvest site morbidity, and surgeon preference. Spontaneous bony closure of small skull defects is known to occur in animal models without bone grafts, but this phenomenon has been unexplored in the human skull base. The objective of this study was to evaluate osseous skull base closure in patients undergoing endoscopic repair of skull base defects. A retrospective review was performed on 13 patients who underwent endoscopic repair of skull base defects with free bone grafts who were followed with postoperative computed tomography scans. This cohort was compared to postoperative radiology from patients undergoing transsphenoidal surgery without rigid reconstruction to evaluate for spontaneous osseous closure of sellar defects. Free bone grafts are incorporated into the bony skull base in the majority of patients (84.6% with at least partial incorporation) at mean of 5.3 years postoperatively. By comparison, patients undergoing pituitary surgery did not demonstrate spontaneous osseous closure on postoperative imaging. Human anterior skull base defects do not appear to spontaneously close, even when small, suggesting that there is no "critical size defect" in the human skull base, in contrast to the robust wound healing in animal models of skull convexity and mandibular defects. Free bone grafts incorporate into the skull base over the long-term and may be utilized whenever a rigid skull base reconstruction is desired, regardless of the defect size.