We performed the first in utero correction of a unilateral right coronal craniosynostosis using 70-day gestation fetal lambs. The craniosynostosis was created in eight fetuses by excising their right coronal sutures, and then placing demineralized bone powder, transforming growth factor-beta, and bone morphogenetic protein-2 into the defect. Twenty-one days later, after suture fusion had occurred, four of the eight sheep were treated with a 4 mm x 12 mm strip craniectomy to open the entire synostosed right coronal suture. The edges of the excision were wrapped with 100-microm-thick Gore-Tex (W. L. Gore & Associates, Flagstaff, Ariz.) sheets to prevent bony refusion. All eight lambs then progressed to term (140 days). The skulls of four normal, unoperated, term lambs were used as controls. At 140 days, all four treated lambs had a widely patent strip craniectomy site without any evidence of bone regeneration. This in utero correction led to a marked improvement in craniofacial morphology of three of four animals when compared with the uncorrected controls with significant (p < 0.01) correction in orbital position, skull length, and shape of the frontal bone. This was in sharp contrast to the uncorrected animals, which had marked orbital elevation, compression of the anteroposterior length of the cranial vault, frontal bone flattening, and shortening of the cranial base. The fourth corrected animal also showed evidence of improvement but had some abnormal calvarial changes secondary to the development of horns, which displaced the calvaria in a downward vector. We conclude that the in utero correction of craniosynostosis is feasible and provides a significant benefit by decreasing the severity of many of the associated deformities seen with this disorder.