This study was undertaken to investigate the histopathologic events of the dural reparative process. Uniform 2-mm dural defects were created in adult beagles, repaired, and then examined in a 6-week period. Primary fibroblastic bridging of the durotomy was not seen until Postoperative Day 6, and it was not until Postoperative Day 10 that ablation of this defect was uniformly seen. Cerebrospinal fluid egress through the dural defects was prevented in the vast majority of cases by the formation of an internal patch composed of proliferative elements of pia and arachnoid mater.