A Developmental Gerstmann syndrome in a 7 years-old-boy with hyperactivity, short attention span, acalculia, agraphia, right-left confusion, finger agnosia and constructional apraxia is reported. An initial trial with methylphenidate was done with good improvement regarding hyperactivity, attention span and constructional apraxia. In the clinical course developed a cerebellar syndrome and intracranial hypertension. Surgical exploration of the cerebellum discovered a medulloblastoma. The author believes that this is the first described association of Developmental Gerstmann syndrome and cerebellar neoplasia. The clinical findings, the etiology and the topography of the Gerstmann syndrome are discussed.