Recognizing cognitive deficits and psychiatric disorders in patients with autosomal dominant ataxias is relatively new. At this time, the percentage of patients with these disorders who experience changes in cognition or psychiatric symptoms is unknown. Cognitive impairment, when seen, is often found on tests of executive function, probably reflecting disruption of afferent and efferent pathways of the prefrontal cortex and subcortical structures, including the cerebellum. Widespread global dysfunction does occur in some cases, especially later in the disease course. Psychiatric symptoms including depression, aggression, irritability, and psychosis have all been reported. As these behavioral changes receive further study, one hopes that guidelines for treating these symptoms will emerge. Clinicians should be mindful of the psychosocial effects that genetic testing for the hereditary ataxias may have, especially in cases of predictive testing for those who are asymptomatic but at risk because of family history. Guidelines established for genetic testing in HD may be helpful when approaching these cases.