The study is examining brain volumes and psychological measures in a population of patients with Huntington's disease (HD) who have been followed longitudinally. The specific aim of the project is to determine the relationship between subcortical brain volumes and the pattern and rate of cognitive decline. This is a unique project in which we have successfully interpreted a variety of neurocognitive, psychologic, and neuroanatomic data on 114 HD patients and 47 mutation- negative control subjects. As we continue to collect data annually, we hope to further and more specifically define predictors of impairment and patterns of decline over the course of the illness.