The present study was carried out to quantify the subsequent vascular regeneration around a lesion cavity made in the rat cerebral cortex and to decide the origin of the regenerated microvessels. A quantitative study utilizing computerized image analysis after microvascular perfusion with India ink indicated approximately 25 and 160% increase of the vascular density adjacent to the cavity compared to the contralateral cortex at 4 and 21 days, respectively, after lesioning. The microvasculature around the cavity was also evaluated by scanning electron microscopy of vascular corrosion casts. Newly formed leptomeningeal vessels began to grow down toward the floor of the cavity 4 days after lesioning and nearly covered the walls of the cavity 21 days after lesioning. A neovascular network of leptomeninges and connective tissue (e.g., dura) was formed as a roof over the cavity. Numerous branches of these newly formed vessels and prominent anastomoses with the capillary network in the walls and floor of the cavity were observed. Newly formed vessels also originated from the choroid plexus in cases where the lateral ventricle had been opened at the time of lesioning. These results document the plasticity of the vascular system in the cerebral cortex after a mechanicalinjury. The regenerated vascular network may offer a suitable condition for survival of transplanted tissues.