The use of guided bone regeneration to fill large bone voids in the mandible created through en bloc resection and chronic granulation in three primates was examined. In each of three animals, en bloc resections of implants and surrounding bone were done bilaterally (10 × 8 mm and 16 × 8 mm). Tissues were allowed to heal in a chronic state (for 6 months). A reinforced expanded polytetrafluorethylene (e-PTFE) membrane was then surgically placed over each defect site to be followed for 1 year postsurgically. Two of the six membranes became infected during the first month and were removed. The remaining four membranes were removed en bloc after 1 year. Bone regeneration (greater than 90% of the defect) was observed clinically, and subtraction radiology demonstrated bone gain of between 544 and 733 mg. Histomorphometry after fluorescent labeling demonstrated a mean growth rate of 2.77 µm/wk for all sites measured, and a decrease in the number of osteons from the new bone at the crest to the mature bone at the base of the original defect. This study gives evidence that substantial quantities of new bone can be produced in atrophic mandibles and that this regenerated bone exhibits normal maturation dynamics. Keywords: guided bone regeneration, mandibular defects, monkeys