Cerebellar involvement in tuberous sclerosis is rare and generally nonsymptomatic. The authors describe a cerebellar tuber in a 5-year-old boy with tuberous sclerosis. A CT scan at age 2 years showed the characteristic cortical, white matter, and subependymal lesions of tuberous sclerosis. At 5 years, when the patient was symptomatic with ataxia, the CT and MRI scans revealed additionally the presence of a right cerebellar enhancing lesion with edema. A total surgical resection was undertaken. The cerebellar lesion was very firm and demonstrated marked disorganization of neuronal architecture in the cerebellar folia, with bizzare ectopic neurons in the molecular and granule cell layers and white matter, along with calcification, gliosis, and Rosenthal fiber deposition. Balloon cells with glassy, pale, eosinophilic cytoplasm were also present. There was a marked loss of myelin in the white matter, with significant vacuolation and gliosis. Electron microscopy documented abundant lysosomal inclusions, prominent rough endoplasmic reticulum and Golgi complexes, microtubules, intermediate filaments, and synaptic contacts. While there is much speculation as to the precise nature of cerebellar pathology in tuberous sclerosis, this case demonstrates conclusively that the cerebellar lesions reflect anomolous neuronal development and migration akin to supratentorial lesions and can rarely be symptomatic.