A heterogeneous group of neurological disorders known as the spinocerebellar ataxias (SCA) are characterized by degeneration of the cerebellum, spinal cord and brainstem. We describe linkage analysis in four unusual SCA families revealing a distinct disease locus on chromosome 3p14-21.1. The disease in these families is distinguished from other forms of SCA by concomitant retinal degeneration. Initial visual problems leading to blindness, disabling ataxia and anticipation are seen in all kindreds. The anticipation in these families suggests a dynamic mutation at this locus. Eventual molecular characterization of this disease may provide valuable insights into the processes of both neural and retinal degeneration.