Spino cerebellar ataxia (SCA) are a complex group of hereditary neurodegenerative disturbances of autosomal dominant pattern. They are largely characterized by the clinical presence of cerebellar ataxia related to ophtalmoplegia, dysarthria, pyramidal and extra-pyramidal signs and loss of deep sensitivity. SCA 7 belongs to the SCA group in which the disturbance is a result of the expansion of CAG triplet repetition located in the 3p12-p21 chromosome. The characteristic clinical feature of SCA7 is the loss of visual acuity and blindness. We present here three cases of ataxia, from the same family, with loss of visual acuity and other neurological disorders. The diagnosis was confirmed by a genetic analysis of the index case in whom the characteristic genetic abnormality of SCA7 was discovered. To our knowledge, this is the first case of SCA7 confirmed by genetic study in Argentina. Only two other reports on family cases were found in a review of the literature of Latin America up to January 2006. The purpose of our report is to draw attention to the diagnosis of this degenerative disease in patients with progressive cerebellar ataxia associated with loss of visual acuity symptoms, where a positive family history is found.