This report describes a multilobular ameloblastoma that invaded the left mandible of a 31-year-old pony. The pony presented initially with a palpable mass that protruded from the left mandibular region. Ante mortem radiographs of the mass revealed an invasive, multilobular, bony mass with significant loss of dentition. One month following initial diagnostic work-up, the pony was subjected to euthanasia due to unrelated clinical signs of colic, secondary to a strangulating lipoma. Magnetic resonance imaging (MRI) of the head was performed post mortem to further characterise the mass and determine the extent of its invasion. The macroscopic and histopathological morphology and immunohistochemical properties of the neoplastic cells strongly supported a diagnosis of a multi-cystic ameloblastoma. To the authors' knowledge, this is the first report of an MRI of an ameloblastoma in the horse.