OBJECTIVE: The aim of the study was to examine the relationship between age at onset of Alzheimer's disease and demographic and clinical characteristics in a large cohort of patients with Alzheimer's disease. METHOD: The subjects were 104 patients meeting the criteria for Alzheimer's disease of the National Institute of Neurological and Communicative Disorders and Stroke. The relationships of age at disease onset to cognitive and noncognitive variables and to rate of progression were explored by using multiple regression analysis. RESULTS: Earlier disease onset was associated with the presence of greater language and praxis difficulties and with the development of higher depression scores during the follow-up study period but not with faster disease progression. CONCLUSIONS: These findings suggest that in Alzheimer's disease, which is a clinically heterogeneous illness, younger age at onset may be related to the presence of more prominent language and praxis impairment and to development of greater depression during the disease course.