We have studied 10 Huntington's disease (HD) outpatients to investigate the relationship between chorea and the psychiatric manifestations of this disease. We used neuropsychological tests sensitive to memory and diffuse cerebral dysfunction and a new, simple, objective test of chorea to study the relationship between chorea and dementia. Using SADS/DSM-III diagnoses, we replicated previous findings of the high prevalence of psychiatric disorders associated with HD. A new finding in this study was the strong relationship between the severity of chorea and that of dementia, particularly regarding memory loss. Implications of this finding are discussed in light of the neuroanatomy of the basal ganglia and frontal lobes.