Senile chorea (SC) is characterized by the presence of late onset, generalized chorea with no family history and no dementia. It is unclear whether it is a distinct clinical entity or represents late onset Huntington's disease (HD) with an undetected family history. In order to clarify this issue, we carried out a prospective, multicenter study of suspected cases of SC. Since 1994 we identified six cases that met clinical criteria for SC. Their study included routine lab tests, cerebral MRI, neuropsychological assessment, and lastly gene IT15 analysis. An abnormal expansion of the (CAG)n repeat was found in three patients. Although there were no criteria for dementia, most neuropsychological tests revealed mild to moderate deficits, particularly in visuospatial and prefrontal tasks, m all six patients, those that were finally diagnosed as having late onset "sporadic" HD, but also in patients that finally had SC. This study provides further evidence on the existence of SC; however, the distinction from late onset "sporadic" HD seems not to be possible on clinical grounds unless a genetic study is carried out. Some cases of suspected "SC" have late onset "sporadic" HD.