Executive deficits characterize the initial phases of Alzheimer disease (AD) and mild cognitive impairment (MCI), and are clinically correlated to neuropsychiatric symptoms and functional loss. The aim of this study was to determine the accuracy of the Behavioral Assessment of the Dysexecutive Syndrome test (BADS) for comparing the performance between patients with amnestic MCI (aMCI) and mild AD and for detecting early signs of alterations in executive functions. BADS was performed on 60 healthy controls, 20 patients with aMCI, and 40 mild probable AD patients (20 early-onset AD patients and 20 late-onset AD patients). Significant differences in battery performance were found among groups on the BADS subtests Rule Shift Cards, Program of Action, Zoo Map, 6 Modified Elements, and 3 total scores. Early changes in executive functions were detected in both AD (irrespective of age of onset) and aMCI patients. The BADS proved useful for differentiating between these patient groups. Our results confirmed the presence of early alterations in executive functions among aMCI and mild AD patients.