To study the effect of interposed periosteum on physeal fracture healing, 52 skeletally immature female Harlan Sprague-Dawley rats, 4 to 5 weeks of age, were randomized to one of three cohort groups. All animals underwent surgical dissection of the left proximal medial tibia; dissection consisted of superficial exposure and incision of a standard periosteal flap. Animals in Group I (fracture alone) underwent physeal fracture; those in Group II (fracture and periosteum) underwent physeal fracture with interposition of periosteum in the fracture site, and those in Group III (positive control) underwent physeal fracture, excision of 1/2 of the growth plate, and interposition of periosteum in the defect. After histologic examination of serial sections, fracture alone resulted in physeal injury frequently associated with small bar formation without a reduction in leg length. With the addition of interposition of periosteum into the fracture site, a small, but statistically significant, increase in leg length discrepancy frequently associated with small histologic bar formation occurred when compared with fracture alone.