A pediatric patient presenting with an open forearm fracture with segmental defect is rare, and the pediatric orthopedic literature to guide treatment is sparse. There are several described methods to treat the defect, including bone grafting and bone transport techniques. In addition, there are reports of fibular regeneration after resection if the periosteum is left intact. We present a case report of complete regeneration of over half of a pediatric radial shaft with an intact periosteum, after traumatic extrusion from an open fracture. A 6-year-old girl presented with a Gustilo Grade-IIIB open fracture with extrusion and loss of 7 cm of her radial shaft. Initially, the arm was stabilized using a monoplanar external fixator. She developed a compartment syndrome and underwent volar forearm fasciotomies. We found her periosteum grossly intact and decided to allow its natural biology to provide healing potential for the radial defect. She was placed into a circular external fixator, leaving her wrist and elbow free, and her ulna was stabilized with a flexible intramedullary nail. Soft tissue coverage was obtained with a split thickness skin graft. The patient’s skin graft healed uneventfully and there were radiographic signs of bone regeneration by 2 weeks postoperatively. She maintained most of her elbow and wrist motion while in her external fixator. She developed a small pin site infection that resolved with oral antibiotics. By 10 weeks postoperatively, radiographs showed adequate corticalization and the fixator was removed. By 8 months postoperatively, the patient was released to full activity with nearly full function and range of motion. Our patient sustained a severe and rare injury but had an excellent outcome with minimal complications. This report represents a method of treatment for large bony defects in children if the periosteum is grossly intact, as opposed to more complex procedures. The intact periosteum can regenerate bony defects in the forearm if stabilized appropriately. Level of Evidence: Level 4; case report.