The objective of this paper was to evaluate, histologically, the tissue reaction in the chin after a vertical augmentation using interpositional porous polyethylene (PPE) implants in monkeys. Six monkeys (Sebus apella) underwent an anterior horizontal mandibular osteotomy with implantation of an interpositional PPE implant to increase the vertical height. The animals were sacrificed 5 months postoperatively. Histologic preparations were stained with hematoxylin and eosin. The perimeter of the interface between the implant and the bone, the implant and the trabecular space, and the implant and the fibrous capsule were quantified using the NIH Image Analysis System (Image 1.60/PPC). In addition, the Tukey test was done. The study demonstrated that bone growth takes place within the pores of the implant; a fibrous capsule exists in some animals, where the implant has contact with the periosteum and mentalis muscle with few chronic inflammatory cells; and the 3 different tissues responded in statistically different manners. Perimeter analysis revealed 68.9% implant-bone contact, 22.9% implant-fibrous tissue contact, and 8.2% implant-trabecular space contact.