This chapter provides an overview of Spinocerebellar ataxia type 1 (SCAl). SCAl is an autosomal dominant neurodegenerative disease typically with mid-life onset characterized by motor symptoms in the absence of cognitive deficits. SCAl is a member of an intriguing group of neurodegnerative disorders known as the polyglutamine diseases. At the present, nine diseases are shown to result from expansion of CAG repeats coding for polyglutamine tracts in the respective proteins. These disorders include spinobulbar muscular atrophy (SBMA), Huntington's disease (HD), spinocerebellar ataxias, and dentatorubropallidoluysian atrophy (DRPLA).Expansion of the polyglutamine tract in the SCAl encoded protein, ataxin-1, results in an alteration in its folding. A key aspect of SCAl pathogenesis is localization of mutant ataxin-1 to the nucleus.