The authors report on a 17-year-old boy who suffered from slowly progressive and long-standing symptoms of ataxia, neck pain, and headache. Computerized tomography (CT) and magnetic resonance (MR) imaging revealed a tumor arising from the floor of the fourth ventricle that resulted in a moderate hydrocephalus. A partial resection was performed. Histological and immunohistological findings led to the diagnosis of an atypical central neurocytoma of the fourth ventricle. The imaging features on CT scanning, MR imaging, and proton MR spectroscopy studies, the clinical picture, and the prognosis of this very unusual tumor are discussed. Three cases of neurocytomas in the posterior fossa have been described to date; however, in all three cases some atypical aspects were present. In the present case, with the exception of the very unusual location, both imaging findings and clinical history perfectly met the definition of this rare tumor.