A 4(3/4)-year-old male with Down syndrome (DS) presented with unsteady gait and fatigue. Neuroimaging revealed a cerebellar mass with concomitant obstructive hydrocephalus and additional metastatic lesions. He was successfully treated and is still in complete remission 5 years from diagnosis. The present case illustrates that, although not yet reported, medulloblastoma can also occur in patients with DS.