A six-year-old border collie was presented with a solid mass on the dorsal cranium. Histological examination showed the mass to be a multilobular tumour of bone. A magnetic resonance imaging scan confirmed deformation of the dorsal cranium with compression of the cerebral hemispheres. A craniotomy was performed to excise the mass and overlying skin, resulting in a substantial deficit of calvarium and skin. A cranioplasty using a small intestinal submucosal (SIS) graft was performed to reconstruct the calvarial defect. A local myocutaneous advancement flap was elevated and positioned over the cranioplasty to close the skin deficit. The outcome of this reconstruction was aesthetic and functional. The small intestinal submucosal graft provided satisfactory mechanical support and was a suitable physical barrier in place of the calvarial bone. Histological examination of the small intestinal submucosal graft 128 days after implantation showed that the graft had been replaced by a dense network of collagenous tissue, with small focal areas of partially mineralised woven bone merging with a fibrocartilaginous matrix of the deeper margin. Histological examination also confirmed regrowth of the multilobular tumour of bone in the region of the small intestinal submucosal graft indicating that it is only a suitable implant if adequate surgical margins are obtained.