Clinical subtypes of dementia of the Alzheimer type were evaluated by comparing age at onset, aphasia, family history, and motor disorder in 146 individuals with progressive dementia. Early onset was significantly associated with more prevalent and more severe language disorder. Forty-five percent of all probands had familial history of dementia, but we could not differentiate relative familial risk based on age at onset or aphasia. Independent of duration of illness, myoclonus and noniatrogenic extrapyramidal disorder were associated with greater severity of dementia.