Early-onset Alzheimer's disease (EOAD) beginning before the age of 65 may differ from late-onset AD (LOAD) in clinical course and frequency of nonamnestic presentations. In a 10-year retrospective review, 125 patients with EOAD, diagnosed clinically and verified by functional neuroimaging, were compared with 56 patients with LOAD and further classified depending on predominant cognitive difficulty on presentation. Eighty (64%) of the patients with EOAD had a nonamnestic presentation, compared with only 7 (12.5%) of the patients with LOAD. Compared with LOAD, the patients with EOAD had a shorter duration with lower Mini-Mental State Examination scores. The neuroimaging reports among the patients with EOAD showed more hippocampal atrophy with an amnestic presentation, more left parietal changes with impaired language presentations, and more right parietal and occipital changes with impaired visuospatial presentations. These findings indicate that EOAD differs from LOAD in a more aggressive course and in having predominantly nonamnestic presentations that vary in neuropathological location.