A 4 kg Chihuahua was presented with seizures and a large mass on his dorsal cranium. The mass had regrown after two previous attempts to remove it. Histological examination had shown the mass to be a multilobular osteochondroma (osteochondrosarcoma). A CT scan revealed destruction of the dorsal cranial bones by the mass and compression of cerebral cortex. A craniotomy was performed to excise the mass and attached skin, leaving a large deficit of calvarial bone and skin. A cranioplasty was performed in situ, using polypropylene mesh and polymethyl methacrylate. A caudal auricular axial pattern flap was placed directly over the cranioplasty to fill the skin defect. This unusual reconstruction resulted in good recovery, function and cosmetic effect, although tumour regrowth was seen within the cerebral cortex.