A 3‐year‐old spayed female German Shepherd dog was presented for investigation and treatment of a firm slow growing mass over the right surface of the skull. Computed tomography (CT) of the head revealed a proliferative, rounded and well‐defined compact bone mass expanding extracranially. A right rostrotentorial craniectomy was performed with ‘en bloc’ mass resection. To achieve clear margins, the excision of the outer table of the frontal bone, with subsequent opening of the right frontal sinus, was necessary. To provide an appropriate sealing between the cranial cavity and the nasal cavity, thereby preventing future complications, a cemented partial obliteration and reconstruction of the right frontal sinus was performed. The dog recovered uneventfully. Histopathological analysis confirmed complete resection with clear margins and the final diagnosis of an osteoma. The dog was progressing with no clinical signs 8 months after the surgery.