Forty-six nonconsecutive patients undergoing orthognathic surgery in whom blocks of coralline, porous hydroxyapatite (Interpore-200) were used in lieu of interpositional bone grafts are the subjects of this report. Surgical procedures included inferior repositioning of the maxilla (7) and chin (12), maxillary advancements in cleft (4) and noncleft individuals (13), and transverse maxillary expansions (12). Patients included in this study were only those in whom bone grafts would have been harvested had hydroxyapatite not been available. A total of 93 anatomic sites were implanted. The complication rate attributable to the use of the implant was 4.3 percent. Follow-up period ranged from 6 to 20 months, with a mean of 9.3 months. At this time, osseous stability was confirmed cephalometrically in all but two patients undergoing maxillary expansions. The biologic behavior and mechanical properties of coralline-derived, porous, block hydroxyapatite are discussed. These implant characteristics make it a feasible bone graft substitute for interpositional use in orthognathic surgery. Proper indications for its use as well as technical details to minimize complications are stressed.