A well-demarcated mass was found by computed tomography in the left cerebellar hemisphere of a 4-year-old male Boxer with acute onset of progressive central vestibular syndrome. At necropsy, the pink, gelatinous mass was in the flocculonodular lobe. Histologically, neoplastic tissue arose from the granular layer of the cerebellar cortex and consisted of sheets of oval to round hyperchromatic cells, consistent with the diagnosis of medulloblastoma. Synaptophysin and neuron-specific enolase immunoreactivity supported the neuronal origin of the neoplastic cells; furthermore, a weak to moderate c-kit expression was detected, as reported in pediatric medulloblastoma. Telomerase activity of tumor cells was demonstrated by immunohistochemistry and by the telomere repeat amplification protocol, suggesting involvement of this enzymatic pathway.